1 It was right indeed, most beloved, that we should rather hear our Brother, my colleague, when present before all of us. And just now he refused not, but put us off; for he extorted from me that he might now listen to me, on the condition that I also may listen to him, for in charity itself we are all listening unto Him, who is our One Master in heaven. Attend therefore to the Psalm, entitled A Song of Degrees; considerably longer than the rest under the same title. Let us not therefore linger, save where necessity shall compel us: that we may, if the Lord permit, explain the whole. For you also ought not to hear everything as men untaught; ye ought in some degree to aid us from your past listenings, so that it may not be needful that everything should be declared to you as though new.
2. “Lord, remember David, and all his meekness”. David according to the truth of history was one man, king of Israel, son of Jesse. He was indeed meek, as the Divine Scriptures themselves mark and command him, and so meek that he did not even render evil for evil to his persecutor Saul. He preserved towards him so great humility, that he acknowledged him a king, and himself a dog: and answered the king not proudly nor rudely, though he was more powerful in God; but he rather endeavoured to appease him by humility, than to provoke him by pride. Saul was even given into his power, and this by the Lord God, that he might do to him what he listed: but since he was not commanded to slay him, but had it only placed in his power (now a man is permitted to use his power), he rather turned towards mercy what God gave him....The humility of David is therefore commended, the meekness of David is commended; and it is said to God, “Lord, remember David, and all his meekness.” For what purpose? “How he swore unto the Lord, and vowed a vow unto the Almighty God of Jacob”. Therefore remember for this, that he may fulfil what he has promised. David himself vowed as though he had it in his power, and he prays 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 has vowed. He who exhorts you to vow, Himself aids you 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 dispatched 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 wars against, and conquers....What then does he mean, “How he swore,” etc.? Let us see what vow is this. We can offer God nothing more pleasing than to swear. Now to swear is to promise firmly. Consider this vow, that is, with what ardour he vowed what he vowed, with what love, with what longing; nevertheless, he prays the Lord to fulfil it in these words, “O Lord, remember David, and all his meekness.” In this temper he vowed his vow, and there should be a house of God: “I will not come within the tabernacle of mine house, nor climb up into my bed”. “I will not suffer my eyes to sleep, nor my eyelids to slumber”. This seems not enough; he adds, “Neither the temples of my head to take any rest, until I find out a place for the Lord; an habitation for the God of Jacob”. Where did he seek a place for the Lord? If he was meek, he sought it in himself. For how is one a place for the Lord? Hear the Prophet: “Upon whom shall My Spirit rest? Even upon him that is poor and of a contrite spirit, and trembles at My words.” Do you wish to be a place for the Lord? Be thou poor in spirit, and contrite, and trembling at the word of God, and you will yourself be made what you seek. For if what you seek be not realized in yourself, what does it profit you in another....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)