John Calvin Commentary Psalms 111:9

"He hath sent redemption unto his people; He hath commanded his covenant for ever: Holy and reverend is his name." — Psalms 111:9 (ASV)

He sent redemption to his people. What He had already stated is repeated here in different words. Since the deliverance of His people was the commencement of their salvation, it is introduced first. Next, its confirmation in the Law follows, which is why God’s adoption could never fail.

For although, long before this, God had established His covenant with Abraham, which was also the basis for the redemption of the people, what is mentioned here refers exclusively to the Law. By the Law, the covenant was ratified, never to be annulled.

The point is that, in the deliverance of the people, God did not act the part of a beneficial father merely for a day. Instead, in the promulgation of the Law, He also established His grace, so that the hope of eternal life might continue forever in the Church.

Moreover, you must pay careful attention to what I have cautioned you against elsewhere, a point I will address in more detail when discussing Psalm 119, where the Law is spoken of. The commandments must not always be taken abstractly. This is because the Holy Spirit, in a special way, refers to the promises that are in Christ, by which God, in gathering His chosen people to Himself, has begotten them again to eternal life.