John Calvin Commentary Psalms 119:57

"Jehovah is my portion: I have said that I would observe thy words." — Psalms 119:57 (ASV)

You are my portion, O Jehovah! The meaning of this clause is doubtful, because the term Jehovah may be interpreted either in the nominative or vocative case, and the phrase, I have said, may relate either to the former or latter part of the verse. One reading then is, Jehovah is my portion, and, therefore, I have resolved to observe Your law. Another is, O God! who are my portion, I have resolved to observe Your law. A third is, I have said, or have resolved, that God is my portion, in order to observe His law. A fourth is, I have said, or have resolved, O Lord! that my portion is to observe Your law; and this is the reading of which I approve.

The following interpretation is quite applicable: that God being our portion should animate and encourage us to observe His law. We have already noted in several other passages that God is called the heritage of the faithful, because He alone is sufficient for their full and entire happiness. And since He has chosen us for His special possession, it is only reasonable on our part that we should rest satisfied with Him alone. If we do this, our hearts will also be inclined to keep His law; and, renouncing all the lusts of the flesh, our supreme delight and firm resolution will be to persevere in this.

I have already said that this interpretation is not inconsistent with the scope of the passage and that it provides a very useful doctrine. But the last and fourth reading, which I noted I approved of, is simpler—I am fully persuaded that my best portion consists in keeping God’s law. This accords with the saying of Paul, Godliness is the best gain (1 Timothy 6:6). David here draws a comparison between the keeping of the law and the imaginary good that captivates the ambition of mankind. “Let everyone covet what seems good to him and revel in his own pleasures; I have no ground to envy them, provided I retain this as my portion: the complete surrender of myself to the Word of God.”