The Psalms have been used by the people of God for centuries as part of their praise and worship. However, there are some problem passages - the so-called impreccatory Psalms. Here's a short take on the issue.
The violent imprecations in Psalms 69 and 109 at first appear at odds with passages such as Mt 5.33-34. However, these Psalms are not cries for personal vengeance written in the heat of the moment, or examples of sympathetic magic, but prayers and pleas addressed to God calling for His justice.
David was a righteous man. He was concerned that his own behaviour would not cause offence (69.5); he trusted in God (69.6), praised Him (69.30, 109.30) and waited for His good time to rescue (69.13). David suffered without cause (69.2, 109.3), offering love and prayers to his enemies, but being hated in return (109.4-5 cf. Rm 12.17-19).
David was closely identified with the temple and the things of God, so that his enemies were God’s enemies. He was not a private person but God’s representative, his anointed King. The reproach that was on him was for God’s sake (69.7); he was insulted because of his zeal for God’s house (69.9) and mocked for his piety (69.10-11). Those who spoke evil against him were to be cursed (109.17-18 cf. Gen 12.3) for God’s names sake (109.20-21). This is the justice of the covenant making God.
These passages cannot be dismissed as inferior Old Testament morality, for they find their fulfilment in the New Testament. Jesus is the representative of God par excellence, the one greater than David. His suffering on the cross (Jn 19.28-29) was the fulfilment of the suffering in Ps 69.19-21, for what David was offered in metaphor, Jesus was offered in fact. His mission was not to please himself but to serve God with a zeal for Him and his house, and hence to suffer (69.9 cf. Jn 2.17 and Rm 15.3).
Furthermore, the curse of Ps 69.22-23 is upon Israel for their rejection of the Messiah (Rm 11.9-10). Ps 69.25 and 109.8 are applied to Judas for his betrayal of Jesus Acts 1.20). These passages express the seriousness of rejecting God. Any modern absence of indignation at sin is an alarming symptom.
Finally, the imprecations of the Psalter find an eschatological fulfilment. As expressions of justice before a fully developed eschatology appeared, judgement was this worldly, cursing the good things of life (69.23-4), such as posterity (109.9-15). The martyrs now await God’s vindication (Rev 6.9-11), which will occur on the day of God’s wrath (v17). The final curse will be ejection from Christ’s presence (Mt 25.46). David’s call for his enemies to be blotted out of the book of life (69.28), that is the community of God’s living people, is fulfilled in the resurrection judgement (Rev 3.5, 13.8, 17.8, 20.12).
Because of the new thing done in Christ, forgiveness of enemies is possible (Mt 5.44 cf. Rm 12.14). Our ministry is to “bless, and curse not’, and let God repay (Rm 12.19 cf. Dt 32.35).