Rabbi Elazar quotes the title verse and proceeds to discuss the righteous ways of King David, who devoted his life to God. David knew that when the northern wind stirs at midnight, God joins the righteous in the Garden of Eden. He also knew that the words of the Torah spoken at night ascend before God. Therefore, he would rise at midnight to sing songs and to praise God. Of all the titles that he gave his songs, "Halleluyah" was the greatest - because the word encompasses both the Name of God and the call to praise Him. Rabbi Elazar then concludes by explaining the meaning of "whole heart" and "the assembly of the upright."
The might and mystical wisdom of King David is stirred up within our soul, as we peruse this passage. Specifically, the Light aroused at midnight through the actions and songs of David, descends into our world, filling our souls and the souls of mankind. This diminishes the spiritual darkness that gives birth to personal and global strife.