109:6-15 The psalmist prayed that God would do several specific things to avenge him. He asked God to return what his enemy was doing to him back on himself. He wanted a wicked man to oppose and accuse him. He wanted God to judge his enemy guilty and to put him to death. He also asked that God punish his wife and children for his wickedness. In the future he hoped no one would remember him and that he would have no descendents.
It seems inappropriate for David to ask God to execute children for the sins of their fathers since God specifically forbade this in the Mosaic Law (Deut. 26:14). Perhaps David prayed contrary to God's will allowing his hatred to get the better of him. This seems unlikely since God preserved his prayer in the Psalter. Even though the Bible records many things that it does not condone there is nothing in this text that would suggest that David was not praying in the will of God. Another explanation is that he was praying in hyperbole. In other words, he did not really mean what he was saying but used extreme language to communicate his strong feelings. However, he did not just make one statement about his enemy's wife and children but developed this desire in considerable detail. This seems to indicate that he meant what he said. I think the best explanation is that David's concern in these requests was his enemy rather than his enemy's wife and children. He said what he did as a punishment on his enemy, not because his hatred of his enemy extended to his wife and children. David seems to have been anticipating various consequences that his enemy would experience because of God's judgment.174
"One might think the punishment should be confined to the individual and that his family should not have to suffer for his crimes. However, in ancient Semitic thought a man and his offspring were inseparably bound together so that the actions of the former could influence the destiny of the latter. Of course, one sees this principle at work in the world every day and, not surprisingly, it permeates the Bible as well."175
109:16-20 Here David gave reasons for his preceding requests. His enemy had practiced all the things David had asked God to do to him. He mercilessly persecuted the needy and the afflicted. He loved to curse other people rather than blessing them. Therefore the psalmist asked God to clothe him with cursing as with a garment and to make it as a belt that surrounded him always.
Sometimes David spoke of his enemy and sometimes of his enemies in this psalm. Evidently more than one person was in his mind. He may have spoken of an enemy in the singular when he thought of one of his enemies, perhaps the most hostile one. On the other hand he may have used the singular to personify all his enemies.
(NT only) to listen to the NET Bible 
