Charles Ellicott Commentary 1 Chronicles 28:9

"And thou, Solomon my son, know thou the God of thy father, and serve him with a perfect heart and with a willing mind; for Jehovah searcheth all hearts, and understandeth all the imaginations of the thoughts: if thou seek him, he will be found of thee; but if thou forsake him, he will cast thee off for ever." — 1 Chronicles 28:9 (ASV)

And thou, Solomon my son. —The king now turns to his heir, urging a whole-hearted service to his father’s God (1 Chronicles 28:9–10).

Know thou. —Regard, have care for (Psalms 1:6).

The God of thy father might mean the God of Israel (compare 1 Chronicles 29:10). But 1 Chronicles 28:20, where David speaks of my God, suggests the simpler meaning, God of David, here. (Psalms 18:6; Psalms 18:22; Genesis 31:42.)

With a perfect heart. —The word shâlçm means whole, sound, unimpaired; the Latin integer. Hence, what is urged is an undivided allegiance, such as is enjoined by the Decalogue. (Compare 1 Chronicles 29:9; 1 Chronicles 29:19; 1 Kings 8:61.)

A willing mind. —For service is not real unless it is voluntary, and so glad as well as free.

For the Lord searcheth all hearts. —Search, i.e., seek (1 Chronicles 28:8 and following). For the thought, compare Psalm 139:1-4; Psalms 139:23; 1 Samuel 16:7; Psalms 94:9; Acts 1:24; Hebrews 4:13. The Searcher of hearts will at once see through an insincere and half-hearted obedience.

And understandeth all the imaginations of the thoughts. —And every fashioning (yēṣer, εἶδος, Bild) or cast of thoughts he discerns (Genesis 6:5; Genesis 8:21).

If thou seek him. —Deuteronomy 4:29. Seeking Jehovah in earnest always results in finding (Isaiah 55:6). Yet the Divine grace is not restricted even by this condition (Isaiah 65:1).

If thou forsake him. —Deliberately and of set purpose, as choosing to live by other laws than His.

He will cast thee off. —A strong word (hizniah), meaning strictly, to reject as noisome or foul-smelling. (Hosea 8:5.) The verbal form hiphil is peculiar to Chronicles. (See 2 Chronicles 11:14; 2 Chronicles 29:19.)