2 The title then of this Psalm is, as usual, a title intimating on the threshold what is being done in the house: “To David himself for the sons of Jonadab, and for those that were first led captive.” Jonadab (he is commended to us in the prophecy of Jeremiah) was a certain man, who had enjoined his sons not to drink wine, and not to dwell in houses, but in tents. But the commandment of the father the sons kept and observed, and by this earned a blessing from the Lord. Now the Lord had not commanded this, but their own father.
But they so received it as though it were a commandment from the Lord their God; for even though the Lord had not commanded that they should drink no wine and should dwell in tents; yet the Lord had commanded that sons should obey their father. In this case alone a son ought not to obey his father, if his father should have commanded anything contrary to the Lord his God. For indeed the father ought not to be angry, when God is preferred before him. But when a father does command that which is not contrary to God; he must be heard as God is: because to obey one's father God has enjoined.
God then blessed the sons of Jonadab because of their obedience, and thrust them in the teeth of His disobedient people, reproaching them, because while the sons of Jonadab were obedient to their father, they obeyed not their God. But while Jeremiah was treating of these topics, he had this object in regard to the people of Israel, that they should prepare themselves to be led for captivity into Babylon, and should not hope for any other thing, but that they were to be captives.
The title then of this Psalm seems from thence to have taken its hue, so that when he had said, “Of the sons of Jonadab;” he added, “and of them that were first led captive:” not that the sons of Jonadab were led captive, but because to them that were to be led captive there were opposed the sons of Jonadab, because they were obedient to their father: in order that they might understand that they had been made captive, because they were not obedient to God. It is added also that Jonadab is interpreted, “the Lord's spontaneous one.”
What is this, the Lord's spontaneous one? Serving God freely with the will. What is, the Lord's spontaneous one? “In me are, O God, Your vows, which I will render of praise to You.” What is, the Lord's spontaneous one? “Voluntarily I will sacrifice to You.” For if the Apostolic teaching admonishes a slave to serve a human master, not as though of necessity, but of good will, and by freely serving make himself in heart free; how much more must God be served with whole and full and free will, who sees your very will?...The first man made us captive, the second man has delivered us from captivity.
“For as in Adam all die, so also in Christ all shall be made alive.” But in Adam they die through the flesh's nativity, in Christ they are delivered through the heart's faith. It was not in your power not to be born of Adam: it is in your power to believe in Christ. Howsoever much then you shall have willed to belong to the first man, unto captivity you will belong. And what is, shall have willed to belong? Or what is, shall belong? Already you belong, cry out, “Who shall deliver me from the body of this death?” Let us hear then this man crying out this.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)