Purport

Continuing from earlier verse where Bhagvan Shri Krishna explained to even a bad person if leaves all his vile conducts of past and chooses the path of virtues and devotion, he qualifies to be considered as Sadhu., here is what Shri Krishna said in earlier Shloka

If one who is given to vile conduct propitiates Me without any distraction then he-should, indeed, be considered noble, he having rightly resolved. (Ch9: Sh30)

Bhagvan further explains why such a person qualifies to be a Sadhu(man of good deeds). Engaging in pure devotion and good actions continuously remove the bad deeds from human and he becomes as pure as a Saint or Sadhu. Such is the power of devotion that even a bad person can be purified. This is the Signification of Bhakti Yoga, the path of devotion that it creates a protection ring around a human being. Once human acquires the pure devotion he then never falls. Over the period his devotion further increases and he is further purified. Thus a human once becomes a devotee of Bhagvan Shri Krishna never falls again. Shri Krishan has given this solemn promise that his devotees never fall, never perish. He only ascends in his further life from whatever position he is at present.