Which is the biggest sin that we should refrain from at all times and which is the greatest good action?

[This question is part of a Mahā Satsaṅga (grand spiritual discussion) between Swami, Shri Parikshit, Smt. Bindiya and Dr. J. S. R. Prasad.]

Swami replied: The biggest sin is to deny the contemporary Human Incarnation due to ego-based jealousy. The greatest good action is conquering ego and jealousy completely and recognizing the contemporary Human Incarnation. This greatest good action yields the eternal spiritual result, which accompanies the soul in all births.