In William Ames’ commentary on the Heidelberg Catechism, he opens by quoting Psalm 4:6-8, which includes these words: “I will lay down and sleep in peace: because Thou alone, O Jehovah, wilt act so that I will dwell securely.” He says the Psalmist writes these words so that he may show that his highest good (summum bonum) is located in God’s favor towards him. Ames goes on to list five lessons we can learn from this text, and from the “comfort” theme of Q/A #1 of the Heidelberg Catechism. I’ve listed them below (without his comments on each lesson):
1) The highest good ought to be considered and sought above all other things in our entire life.
2) The highest good of people in this life cannot be obtained from [earthly] goods.
3) Our true and highest good consists in the union and communion we have with God.
4) The joy that believers gain from the communion that they have with God overcomes, by its own sweetness, all human delights and happiness.
5) This joy and holy consolation convey a certain security to the consciences of the faithful.
As you may have noticed, this could be a commentary on the first Q/A of the Westminster Shorter Catechism as well! You’ll have to get the book to see how Ames explains these five lessons in a biblical, edifying, and pastoral manner: William Ames, A Sketch of the Christian Catechism. I especially appreciate how Ames brings up assurance of salvation in his discussion of our highest good (see #5 above). Like the Heidelberg Catechism says, “Because I belong to him, Christ, by his Holy Spirit, assures me of eternal life!”