Śrīla Bhakti Rakṣak Śrīdhar Dev-Goswāmī Mahārāj explains the necessity of sincerity.
Imitation should always be avoided. We must be sincere. Without sincerity, everything is bogus. Sincerity must be there, whatever.
sarala hale gorāra śikṣā bujhiyā la-ibe
(Śrī Prema-vivarta: 8.3)
“When you are sincere, you will understand Gorā’s teachings.”
yadi bhajibe gorā sarala kara nija mana
(Śrī Prema-vivarta: 8.2)
[“If you want to serve Gorā, make your heart sincere.”]
Be simple, be unassuming, be sincere. Otherwise, everything will be bogus. If you imitate that you are a sādhu, it is gone. Don’t try to imitate, to copy, but really try to be so. Don’t try to copy the external movements of a sādhu, but the inherent thing, the inner thing, try to hit that. Try to acquire the innermost thing. Try to enter into the heart of a Vaiṣṇava and not his figure nor dress. It is difficult, of course, to enter into the heart of a Vaiṣṇava because there is the Temple of the Lord. Still, try to connect and get even a spec, a drop, of the nectar that is within the heart of the Vaiṣṇava, that rasa, a drop of that rasa, is of the highest quality and divinity.
Source
31 August 1981