Ps 131:2

“For what purpose? "How he sware unto the Lord, and vowed a vow unto the Almighty God of Jacob" (ver. 2). Therefore remember for this, that he may fulfil what he hath promised. David himself vowed as though he had it in his power, and he prayeth God to fulfil his vow: there is devotion in the vow, but there is humility in the prayer. Let no one presume to think he fulfilled by his own strength what he hath vowed. He who exhorteth thee to vow, Himself aideth thee to fulfil. Let us therefore see what he vowed, and hence we comprehend how David should be understood in a figure. "David" is interpreted, "Strong of hand," for he was a great warrior. Trusting indeed in the Lord his God, he despatched all wars, he laid low all his enemies, God helping him, according to the dispensation of that kingdom; prefiguring nevertheless some One strong of hand to destroy His enemies, the devil and his angels. These enemies the Church warreth against, and conquereth. ...”