If we want to understand this science... It is science, it is not sentiment. Bhakti-yoga is not sentiment, it is a science. Therefore we have to take it from authorized Vedic instruction. Śrīla Rūpa Gosvāmī has advised that science means you have to take it from the Vedic knowledge.
Lecture on SB 5.5.14 -- Vrndavana, November 2, 1976:
Pradyumna: "As I have advised you, My dear sons, you should act accordingly. Be very careful. By these means you will be freed from the ignorance of the desire for fruitive activity, and the knot of bondage in the heart will be completely severed. For further advancement, you should also give up the means. That is, you should not become attached to the process of liberation itself."
Prabhupāda:
karmāśayaṁ hṛdaya-granthi-bandham
avidyayāsāditam apramattaḥ
anena yogena yathopadeśaṁ
samyag vyapohyoparameta yogāt
[SB 5.5.14]
So, the bhakti-yoga process is described in the previous verses. Real purport is, karmāśayam, how to be free from karmāśayam. So long our mind will be absorbed in karmāśayam, then there is no question of becoming free from this material body. Karmānubandhaṁ na mucyate deha-yogena tāvat. This is already advised, the whole purpose is how to make the spirit soul from the bondage of contamination of repetition of birth and death. That is the purpose of human life. Karmāśayam, everyone is trying to become happy by working hard and getting the result. Ābrahma-bhuvanāl lokāḥ, not only here, but also in other planets up to the Brahmaloka, this process is going on. And to counteract this process, in the previous three verses it has been explained how one can gradually become relieved. The first process is recommended, haṁse gurau mayi bhaktyānuvṛtyā.
So this is the Vedic injunction. If we want to understand this science... It is science, it is not sentiment. Bhakti-yoga is not sentiment, it is a science. Therefore we have to take it from authorized Vedic instruction. Śrīla Rūpa Gosvāmī has advised that science means you have to take it from the Vedic knowledge. Vedic knowledge means there is no mistake, there is no cheating, there is no imperfect senses. Everything is perfect. So science means, which is perfect knowledge. Not perhaps, it may be, that is not science, theory. Theory is not science. Science, the most important items of science is observation and experiment. First of all to study the situation by observation, and then practically, when you are able to make an experiment, then it is science. Otherwise, theoretical knowledge has no meaning.