Because Yahweh’s voice declared that Enos’s sins had been forgiven, we can assume that at least some of his long prayer was spent in recognizing and repenting of those sins. But that is not all. Many are forgiven of their sins without also hearing the voice of the Lord. Therefore, Enos was not only repenting but being called as a prophet. It is to bestow this high calling upon him that Yahweh spoke directly to him. Indeed, a prophetic calling, by definition, demands direct communication.
It is also interesting that Enos does not feel his sins swept away until he recognizes that he believes Yahweh’s declaration. This is an important aspect of repentance, for while the actual removal of sin happens through the power of God (and the miracle of the Atonement), we nevertheless are not truly forgiven until we are able to forgive ourselves. Enos’s sins were already gone from Yahweh’s accounting; but until they were gone from his own, they remained with him as painful remembrances and perhaps even spiritual shame. Enos was able to let them go, however, because of Yahweh’s declaration, and his understanding that Yahweh would not lie.