Bhakti-rasamrita-sindhu compares the love of God to the radiance of the sun in that it never ceases to soften the heart of the devotee, forever established in transcendence, even beyond material virtue. And the process by which the heart is purified more and more under the effect of the sun of divine love is called bhava. Roupa Gosvami (disciple of Lord Chaitanya) explains in this regard that the bhava is held to be the permanent asset of the distinct soul, and that the crucial point of the evolution towards the bhava is what is called marginal love for God. It is when this state, the bhava, becomes deeper and deeper that scholarly devotees give it the name of God's love. According to the Narada-Pancharatra (sacred book):
When one is firmly convinced that Visnu is the sole object of love and worship, and that no other, even a heavenly being, is worthy of devotion, only then does one experience a sense of intimate love towards God. This is what such eminent figures as Bhisma, Prahlad, Uddhava and Narada have to say.
If, as a result of some godly activity that can bring about devotional service, one becomes eager to serve the Lord and seek the company of pure devotees, one will not be long in developing an attachment to singing and listening. As you continue to sing and listen in this spirit, you will always progress more in the devotional service of the Supreme Lord according to the rules. Little by little, the ties and apprehensions linked to the material sphere will then fade. The devotee who progresses in singing and listening in this way sees his initial faith strengthened with each step, until he perceives a real attraction for devotional service which will gradually turn into attachment. When this attachment is purified, it assumes two characteristics, the bhava and the rati, which, as it grows, takes on the name of God's love, the ultimate goal of human life.
Roupa Gosvami sums up this evolution as follows in his Bhakti-rasamrita-sindhu: Faith is the first requisite; it is this which prompts us to seek the company of pure devotees, thanks to which the devotional service develops, able to dispel all our doubts. From then on acquiring a firm conviction, one develops an attraction, then an attachment for devotional service which makes us adhere to the principles which govern it. Beyond that, we end up having access to love for God, to his eternal condition. And this love for God increases and then deepens until it reaches its peak.
In Sanskrit, this ultimate level is called prema, and it is defined as the love of God free from all expectations. The words prema and love are not perfectly synonymous, but it is all the same to say that the prema corresponds to the highest form of love. And the human being who reaches this level is undoubtedly the most perfect of all, as confirmed by the Srimad-Bhagavatam (III.25.25):
It is only through contact with pure devotees that one can conceive of an attraction to Krishna consciousness and, by striving to apply it in one's life, attain the levels of bhava and prema.