A Penitential Psalm
Psalm 38:21 (ESV) … “Do not forsake me, O Lord! O my God, be not far from me!”
PSALM 38 is the third of the Penitential Psalms. These are psalms of confession and sorrow for sin. The two before this are Psalms 6 and 32. The ones that follow are Psalms 51, 102, 130, and 143.
These Penitential Psalms are important because they show us how to confess our sin. David puts into words what we are feeling and teaches us how to come to God. When we are overwhelmed with guilt, we can turn to one of these psalms and make its words our own. This may be one reason why Psalm 51 was recited at the end of the daily morning service in the early centuries of the church.
God often contends with His children to awaken their consciences and to set their sins in order before them for their humiliation. If we are truly penitent for sin, we will make a particular acknowledgment of what we have done amiss and God will then restore the joy of salvation, with patience to bear our affliction.
 Johnston, J. A. (2015). Preaching the Word: The Psalms: Rejoice, the Lord Is King—Psalms 1 to 41. (R. K. Hughes, Ed.) (Vol. 1, p. 387). Wheaton, IL: Crossway.  Brooks, K. (2009). Summarized Bible: Complete Summary of the Old Testament (p. 119). Bellingham, WA: Logos Bible Software.