Many devotees think that BHAKTI is a process of SUBSTRACTION.
A process, where we need to get rid of things that stand in the way of our progress.

It is correct. We need to get rid of many “things” on our journey through bhakti, namely of our “unwanted things” aka “anarthas” (unwanted desires).

This process of subtraction is mainly based on the siddhanta that everything is already “there” within the jiva, the spiritual soul.

But our purva acaryas never mention anywhere that “everything is already within the jiva”.
For those deeply interested in jiva-tattva, please study Anucchedas 19 -47 in Srila Jiva Goswami´s Paramatma Sandarbha.

Some say that bhakti is already there, that prema is already there and some even go as far as to say that the siddha deha is already there…all covered by the jiva´s ignorance…maya-sakti.

Bhakti, prema and the siddha deha are of SVARUPA-SAKTI.
MAYA-SAKTI can never cover SVARUPA-SAKTI.
MAYA-SAKTI can only cover the jiva, TATASTHA-SAKTI.

In reality, bhakti is a process of ADDITION.
It is something that is BESTOWED upon us.
The seed of bhakti is RECEIVED. It is GIVEN.

brahmāṇḍa bhramite kona bhāgyavān jīva
guru-kṛṣṇa-prasāde pāya bhakti-latā-bīja
(Caitanya caritamrta, Madhya 19.151) –

“Wandering throughout the universe, some (kona) fortunate (bhagyavan) jivas by the mercy of Guru and Krishna receive (pāya) the seed of the devotional plant/creeper (bhakti lata bija).”

Bhakti is INFUSED into our hearts by those whose hearts have been infused with bhakti from someone whose heart has been infused….and so on…
Bhakti comes from bhakti. It is a process of mercy.
It is the “good  fortune” of the jivas when they receive the seed of bhakti by the mercy of Krishna THROUGH His devotees.

Bhakti is a process of ADDITION.
We add something most valuable to our lives.

Bhakti is a powerful force, a joined combination of Krishna´s samvit and hladini saktis. It enters our hearts and then it will gradually mature into the most glorious form of pure love, PREMA.

First it is sadhana-bhakti (the bhakti of practice).
Then it becomes bhava-bhakti (the bhakti of spiritual emotions).
Then it becomes prema-bhakti (the bhakti of the purest love).

When we think that our focus must be on getting rid of this and that…this unwanted desire, that unwanted desire, this habit, that habit…we will never attain the higher stages of bhakti. The more we focus of this “stripping down” process, the more we focus on the negative things dwelling within the chambers of our hearts, the more we will block the natural flow of bhakti.

But when we practice bhakti in anugatya of Sri Gurudeva (guru pada ashraya), then, and only then bhakti alone will take care of all “unwanted things”.
No need to focus on the SUBSTRACTION, but instead all focus on the ADDITION.

In our Srimad Bhagavatam we can read:

vāsudeve bhagavati bhakti-yogaḥ prayojitaḥ |
janayaty āśu vairāgyaṁ jñānaṁ ca yad ahaitukam ||
(SB 1.2.7)

Bhakti dedicated to Lord Kṛṣṇa, endowed with special moods, quickly produces detachment from material goals and knowledge of the Lord devoid of the desire for liberation.

To read the commentary written by Srila Vishvanatha Cakravartipad to this verse is very much recommended. [see (1)]

Srila Rupa Goswami writes the following verses in his Bhakti Rasamrita Sindhu:

yad ubhe citta-kāṭhinya-hetū prāyaḥ satāṁ mate |
sukumāra-svabhāveyaṁ bhaktis tad-dhetur īritā || BRS 1.2.249||

Because jñāna and vairāgya generally make the heart harsh, the authoritative devotees have concluded that bhakti alone, whose nature is very tender, is the cause of entering into bhakti.

yathā tatraiva—
tasmān mad-bhakti-yuktasya yogino vai mad-ātmanaḥ |
na jñānaṁ na ca vairāgyaṁ prāyaḥ śreyo bhaved iha ||BRS 1.2.250||

In the Bhāgavatam, it is also said: 

Therefore, for a devotee engaged in My loving service, with mind fixed on Me, the cultivation of knowledge (impersonal) and renunciation is generally not the means of achieving the highest perfection within this world. SB 11.20.31

kintu jñāna-virakty-ādi-sādhyaṁ bhaktyaiva sidhyati ||BRS 1.2.251||

However, the goals of jñāna, vairāgya and other processes are achieved by bhakti alone.

yathā tatraiva—
yat karmabhir yat tapasā jñāna-vairāgyataś ca yat |
yogena dāna dharmeṇa śreyobhir itarair api ||252||

sarvaṁ mad-bhakti-yogena mad-bhakto labhate ’njasā |
svargāpavargaṁ mad-dhāma kathañcid yadi vāñchati ||253||

Thus, it is said in Bhāgavatam:

Everything that can be achieved by fruitive activities, penance, knowledge, detachment, mystic yoga, charity, religious duties and all other means of perfecting life is easily achieved by My devotee through loving service unto Me. If somehow or other My devotee desires promotion to heaven, liberation, or residence in My abode (for service), he easily achieves such benedictions.  (SB 11.20.32-33)

Bhakti will enter our hearts and the more we progress the more all “unwanted things” will be driven out.

Visvanatha Cakravarti Thakura writes in his tika to Srimad Bhagavatam (10.33.39): 

“One who hears and chants about Kṛṣṇa’s rasa-lila, which is the crest- jewel of all pastimes, gets the crest-jewel of all results, namely kṛṣṇa-prema (bhaktiṁ parāṁ).
One who continuously hears (anusrnuyat), glorifies or writes poetry (varnayet) about this autumnal rasa-lila (idam) and similar pastimes of Kṛṣṇa described by other poets (ca), first of all, even if he has the heart disease of material lust, becomes imbued with prema; then, by its effect the disease of the heart is destroyed.”

So, by practicing bhakti (especially hearing and chanting) the heart disease of material lust is DESTROYED.

We don´t have to practice separate ways of “destroying” our heart disease by extreme methods of renunciation for example.

It is like if you have a glass half full with olive oil. If we add lots of water, the oil will spill out and water will remain.

It is the same with bhakti. Bhakti will appear and our “oil” will spill out.

Bhakti is a process of ADDITION and it will lead us to a transformation, not to an elimination.
Bhakti is like a fire, our hearts are like pieces of iron.
By practicing bhakti, our iron hearts will become hearts of gold and then take on the same qualities like the fire.
Bhakti is of svarupa sakti and it will fill up our consciousness with svarupa sakti until we finally attain a spiritual body suitable for our spiritualized consciousness.
Everything will be “accomplished” by bhakti, the combination of samvit and hladini sakti. 

tatra sādhana-bhaktiḥ – “Now sadhana bhakti will be defined”:
kṛti-sādhyā bhavet sādhya-bhāvā sā sādhanābhidhā |
nitya-siddhasya bhāvasya prākaṭyaṁ hṛdi sādhyatā ||  – BRS 1.2.2

“Devotion which is enacted through the senses and which leads
to the self-manifestation of bhāva-bhakti, is called sādhana-bhakti.
The self-manifestation within the heart [of the practitioner] of the eternally existing transcendental affect of devotion (bhāva) is known as the completion stage of devotion.”
(Bhakti Rasamrita Sindhu 1.2.2)

Srila Jiva Gosvami’s Durgama sangamani commentary:

bhāvasya sādhyatve kṛtrimatvāt parama-puruṣārthatvābhāvaḥ syād ity āśaṅkyāha—nityeti |bhagavac-chakti-viśeṣa-vṛtti-viśeṣatvenāgre sādhayiṣyamāṇatvād iti bhāvaḥ

“A doubt may arise that since this state is achieved [sadhya], implying that it is artificially produced, it is not the ultimate goal. The second line responds to this doubt by saying that is is eternal, and simply appears within the heart. That is because its appearance [and not its creation] will be accomplished in the future by the special actions of the most excellent transformations [samvit and hladini aspects] of Bhagavan’s svarupa sakti [which are perfect and eternal].

Srila Visvanatha Cakravarti Thakura’s Bhakti sara pradarsini commentary:

tena dharmārthādi-puruṣārthāntara-sādhaka-bhaktiś ca parākṛtā, uttamāyā eva upakrāntatvāt | bhāvādīnāṁ sādhyatve kṛtrimatvāt parama-puruṣārthatvābhāvaḥ syād ity āśaṅkyāha—nityeti |

bhāvasyety upalakṣaṇaṁ śravana-kīrtanādayo’pi grāhyāḥ |
teṣām api karṇa-jihvādau prākaṭya-mātram, yathā śrī-kṛṣṇo vasudeva-gṛhe’vatatāra |
bhaktīnāṁ bhagavac-chakti-vṛtti-viśeṣatvenāgre sādhayiṣyamāṇatvād iti bhāvaḥ

“This may give rise to the fear that, though bhava bhakti has been mentioned as supreme, it may not actually be the supreme goal of human endeavour, because it is created by sadhana or achieved [i.e. it is not eternal]. The answer is given in the second line. This bhava is eternal, and merely appears within the heart of the devotee. Bhava also includes hearing, chanting and other actions [not just emotions]. These actions of bhava [limbs of bhakti] also appear on the tongue or in the ear, but are not created, just as Krsna appears in the house of Vasudeva. The emotions and actions of bhava are all eternal and spiritual and not material because their appearance in the future will be accomplished by the extraordinary actions of the most excellent transformations [samvit and hladini] of Bhagavan’s svarupa sakti.”

“One can thus understand from this description that bhakti is self-manifesting by nature just like the Lord. There is no other cause for her appearance. Bhakti manifests herself in the devotee by her own independent will.
sādhana bhajana is performed to make the heart suitable for her appearance.”
(Śrī Rādhākuṇḍa Mahānta Paṇḍita Śrī Ananta Dās Bābājī Mahārāja , tika to Mādhurya Kādambinī)

So, the process must not be destroying all things unwanted and substracting all negativity.
The process must be diving deep into the angas of bhakti, most importantly hearing, chanting and remembering what we heard in the association of like-minded and loving Vaishnavas and to serve and take shelter at the feet of the advanced Vaishnavas we meet.

Sri Krishna’s eternal associates always express the desire to please His senses.
This means love is eternally present in them. When the sadhaka’s heart is cleansed by hearing, chanting etc. then the same love flows into this material world like the river Mandakini. It rushes down through the channel of devotees and manifests in our hearts.
Now we can understand that although love does express itself in this world it is never worldly. Love is the characteristic of the transcendental inherent potency of Sri Bhagavan – hladini shakti.

When we perform sadhana, our heart becomes pure. Then bhakti appears in our heart.
When bhakti appears in our heart then we become exceedingly eager for Sri Bhagavan’s darshana.
Bhakti is like blazing fire while the sadhaka’s heart is like gold. The fire (bhakti) melts the especially pure gold (heart) [Srimat Jiva Goswamipad] – in this manner when prema arises, the chitta melts completely and the premika bhakta cries, sings and dances in ecstasy.

 

(1)

Tika from Srila Vishvanatha Cakravartipad on SB 1.2.7:

What form does that satisfaction of the mind take? This satisfaction of the mind is filled with knowledge and experience of the form, qualities and sweetness of the Lord, which cause complete disgust with all inferior objects. That is explained in this verse. This bhakti is endowed (yojitaḥ) in an excellent manner (pra for prakarṣeṇa), with dāsya, sakhya and other loving emotions. Another meaning of bhakti-yogaḥ prayojitaḥ is “bhakti-yoga has been made the only goal (prayojana).” Separate endeavor for attaining knowledge and detachment are not necessary in the practice of bhakti, for bhakti itself produces them. Very quickly (āśu) at the time of performing bhakti, they are attained, for it is said:

bhaktiḥ pareśānubhavo viraktir anyatra caiṣa trika eka-kālaḥ|
prapadyamānasya yathāśnataḥ syus tuṣṭiḥ puṣṭiḥ kṣud-apāyo ’nu-ghāsam ||

Devotion, direct experience of the Supreme Lord, and detachment from other things—these three occur simultaneously for one who has taken shelter of the Supreme Personality of Godhead, in the same way that pleasure, nourishment and relief from hunger come simultaneously and increasingly, with each bite, for a person engaged in eating. SB 11.2.42

There is an objection that if one possesses knowledge, one attains liberation. In answer to this, the verse says that this knowledge is ahaitukam, without motivation for liberation. Ahaitukam comes from hetu, meaning cause or purpose, just as one can say “He lives for eating.” This means “He lives with the goal of eating.” Thus in this verse jnānam ahaitukam means “knowledge without the goal of liberation.” Therefore by practicing bhakti in which knowledge also manifests without the goal of liberation, the liberation of merging does not take place. Knowledge in this case means knowledge and experience of the Lord’s form, qualities and sweetness.
Thus it is said in the Fourth Canto:

vāsudeve bhagavati bhakti-yogaḥ samāhitaḥ |
sadhrīcīnena vairāgyaṁ jṣānaṁ ca janayiṣyati ||

The stage of prema-bhakti completely dedicated to Vāsudeva, produces complete jṣāna and vairāgya. SB 4.29.37

One should practice bhakti with only that goal in mind (sadhrīcīnena), devoid of desire for liberation or other goals. The next verse shows that this type of bhakti is the cause of another type of bhakti.

so ’cirād eva rājarṣe syād acyuta-kathāśrayaḥ |
śṛṇvataḥ śraddadhānasya nityadā syād adhīyataḥ ||

O saintly king! One who hears and studies with faith very soon attains the shelter topics of the Lord to attain prema. SB 4.29.38

Thus it is established in this verse that bhakti alone functions as both the cause and the goal (and not knowledge or detachment).