Psalm 51 has long been regarded as one of the great penitential psalms of our faith. It is the long-standing tradition that King David composed this canticle of sorrow after his affair with Bathsheba and murder of her husband Uriah as a ploy to cover up his sin. The rebuke of the prophet Nathan for his evil actions and the crushing weight of coming to terms with the consequences of what he had done are said to have inspired him to compose Psalm 51 as a reflection of the way his heart had been unbound by the blindness of sin and opened to contrition and penitence.
Each line of the psalm speaks of the ways King David pleaded with God to forgive him of his sins and shaped his heart to be humbler and more sorrowful for his transgressions. Considering King David would have subsequent falls from grace, it is likely he prayed this psalm time and again for the manifold ways he had sinned but confident that God would forgive him if he was truly sorry and resolved to go forth and not sin again.
Priests and religious, who are obligated to pray the Liturgy of the Hours, will pray Psalm 51 every Friday morning. It provides them with a weekly occasion to meditate on the contrite poetry of King David and make the psalm their own in asking God to forgive them for their sins and to have a deeper contrition for their transgressions and more resolved to sin no more.
It could be a fruitful spiritual practice for each of us to try and recite Psalm 51 one a regular basis, perhaps monthly or even weekly to express sorrow for our sins and receive a healthy dose of self-reflection as to where we need to grow in our Christian lives.