From the DepthsBy Rabbi Jack Abramowitz
A Song of Ascents: David says that he called to G-d from the depths, which the Radak says refers to the plight of the Jews in exile. He begs G-d to heed his prayer, saying that if G-d is going to keep an eye on our sins, then we’re done for. G-d has the exclusive ability to forgive sin, a fact that causes Him to be revered.
David longs for G-d. His soul longs for G-d. He prays for G-d’s word. David anticipates G-d’s redemption of Israel even more expectantly than the night watchmen wait for daybreak. David instructs the nation to put their faith in G-d because He is merciful and has large amounts of redemption to go around. He will save Israel from their sins first, then He will redeem them from exile.
The Talmud in Brachos (10b) derives from this Psalm that it is appropriate to pray to G-d “from the depths,” which is why you’ll find in many synagogues that the place from which the leader prays is lower than the surrounding area.