Deep realization in devotional service can only be achieved by the mercy of a Vaisnava. Although many gurus give transcendental instruction to their disciples, real spiritual instructions lead to devotional service. If they don’t, then hearing them is a waste of time: bhagavad-bhakti-hinasya jatih sastram japas tapah apranasyaiva dehasya mandanam loka-ranjanam.
Lectures from a disciple, Vol 1, p. 263. SB 2.3.18, Mayapur, 3.20.1994