The spirit of man is the lamp of the Lord, searching all the innermost parts of his being. (Proverbs 20:27 nasb)
Let us recall that when the spirit of man is brought back into union with God, and the Holy Spirit comes in and fills up that lamp, then that lamp inside man is illuminated and sheds light on his whole inner being. He is no longer in darkness. Furthermore, the reborn spirit becomes a channel through which the Holy Spirit can flow out into this world. Jesus said,
“He who believes in Me, as the Scripture said, ‘From his innermost being shall flow rivers of living water.’” But this He spoke of the Spirit [the Holy Spirit], whom those who believed in Him were to receive; for the Spirit was not yet given, because Jesus was not yet glorified. (John 7:38–39 nasb)
After the Holy Spirit was given on the day of Pentecost, the regenerated spirit of man became a channel or riverbed through which rivers of spiritual life could flow out into this world. That is a marvelous transformation, because just before saying the above, Jesus said, “If any man is thirsty, let him come to Me and drink” (verse 37). So, this transformation of regeneration and the infilling of the Holy Spirit produces a marvelous change—a man who was thirsty, who did not even have enough for himself, now becomes a channel through which waters of spiritual life can flow out to the needy world around him.