PSALM 50 (A Prayer of Repentance)

Have mercy upon me, O God, according to Your lovingkindness; According to the multitude of Your tender mercies, blot out my transgressions. Wash me thoroughly from my iniquity, and cleanse me from my sin. For I acknowledge my transgressions, and my sin before me. Against You, You only, have I sinned, and done this evil in Your sight-- That You may be found just when You speak, and blameless when You judge. Behold, I was brought forth in iniquity, and in sin my mother conceived me. Behold,
You desire truth in the inward part, and in the hidden part You will make me to know wisdom. Purge me with hyssop, and I shall be clean; wash me, and I shall be whiter than snow. Make me hear joy and gladness, that the bones You have broken may rejoice. Hide Your face from my sins, and blot out all my iniquities. Create in me a clean heart, O God, and renew a steadfast spirit within me. Do not cast me away from Your presence, and do not take Your Holy Spirit from me. Restore to me the joy of Your salvation, and uphold me by Your generous Spirit. Then I will teach transgressors Your ways, and sinners shall be converted to You. Deliver me from the guilt of bloodshed, O God, the God of my salvation, and my tongue shall sing aloud of Your righteousness. O Lord, open my lips, and my mouth shall show forth Your praise. For You do not desire sacrifice, or else I would give it; You do not delight in burnt offering. The sacrifices of God are a broken spirit, a broken and contrite heart--these, O God, you will not despise. Do good in Your good pleasure to Zion; build the walls of Jerusalem. Then You shall be pleased with the sacrifices of righteousness, with burnt offering and whole burnt offering; Then they shall offer bulls on Your altar.

Psalm 50 is a psalm of repentance and God's mercy, and a prophecy about salvation through baptism (vv. 2, 7). It is also a teaching about worship in spirit (vv. 17-19). Of all 150 Psalms, this Psalm is the one most used in our Holy Orthodox Church. It is a psalm of repentance said three times daily--Orthros (Matins), Third Hour, and Compline (Apodeipnos)--as well as in every Divine Liturgy, where it is recited by the Priest as a sign of repentance while he censes before the Great Entrance. Historically, this Psalm is Prophet and King David's prayer of confession after his adultery (sin) with Bathsheba (2 Sam. 12:1-15).

http://www.saintandrewgoc.org/blog/2014/1/31/on-the-will-of-god-part-ii.html