The Lord's voice comes to Enos declaring the forgiveness of sins. It is from this that we presume that some of the time of the long prayer was spent in recognizing and repenting of those sins, such that the Lord could declare them removed. Certainly there is more, however, as many have their sins removed without the voice of the Lord proclaiming it, and the sins are just as effectively removed without that spectacular occurrence. What we have in this experience is not only the struggle of Enos, but the call of Enos as a prophet. it is this high calling that warrants the direct communication, indeed, that demands such a direct communication by definition.
It is also interesting that Enos does not feel his sins swept away until he notes that he believes the Lord's declaration. This is an important point for those of us who must repent, 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' sins were already gone from the accounting of the Lord, but until they were gone from his own accounting they remained with him as painful remembrances, and perhaps even spiritual shame. Enos was able to let them go, however because of the Lord's declaration, and his understanding that God would not lie.
So too we, when forgiven, may trust in the word of God that our sins are removed. We may not receive the vocal witness of Enos, but we have witness sufficient in the scriptures and the words of the prophets that we may be free of sin if we truly repent, are baptized and correctly renew those baptismal covenants. We should have no less faith in the word of scripture or modern prophets than did Enos in the voice he heard in the forest.