2 Chronicles 16:9
What is the perfect heart? It must be a different kind of heart to hearts in general. All hearts are not perfect toward God, or else His eyes would not have to be running to and fro throughout the earth to find them. They would be plentiful enough if they were the common sort of hearts. And another thing is evident on the face of the text, that these kind of hearts are very precious in the sight of God.
This cannot mean a merely natural heart; it must mean a renewed heart, because there are no perfect hearts by nature. It must mean, then, a heart renewed by the Holy Spirit, put right with God, and then kept right.
A perfect heart is one in its loyalty to God. It means a heart perfect in its obedience. That man or woman who has this kind of a heart ceases to pick and choose among the commandments of God which he shall obey and which not. He ceases to have his own will, though sometimes he may have a struggle with his own will and the way that God may call him to take.
The partial heart, so common, wants to serve God a little. It is willing to go a little way with God, but not all the way. Can it be expected that the Lord should show Himself strong in behalf of such people?
This perfect heart is perfect in its trust, and, perhaps, that ought to have come first, for it is the very root of all.
How beautiful Abraham was in the eyes of God; how God gloried over him. How do I know that Abraham had a perfect heart towards God? Because He trusted Him. I dare say he was compassed with infirmities, had many erroneous views, manward and earthward, but his heart was perfect towards God. Do you think God would have failed in His promise to Abraham? Abraham trusted Him almost to the blood of Isaac, and God showed Himself strong in his behalf, and delivered him, and made him the Father of the Faithful; crowned him with everlasting honor so that his name, from generation to generation, has been a pillar of strength to the Lord’s people, and a crown of glory to his God.
Catherine Booth, Godliness