And he walked in all the sins of his father, which he had done before him: and his heart was not perfect with the LORD his God, as the heart of David his father.

Jamieson-Fausset-Brown Bible Commentary

3. his heart was not perfect with the Lord . , as the heart of David his father-(Compare 1Ki 11:4; 14:22). He was not positively bad at first, for it appears that he had done something to restore the pillaged treasures of the temple (1Ki 15:15). This phrase contains a comparative reference to David's heart. His doing that which was right in the eyes of the Lord (1Ki 15:5) is frequently used in speaking of the kings of Judah, and means only that they did or did not do that which, in the general course and tendency of their government, was acceptable to God. It furnishes no evidence as to the lawfulness or piety of one specific act.

Matthew Henry's Concise Commentary

15:1-8 Abijam's heart was not perfect with the Lord his God; he wanted sincerity; he began well, but he fell off, and walked in all the sins of his father, following his bad example, though he had seen the bad consequences of it. David's family was continued as a lamp in Jerusalem, to maintain the true worship of God there, when the light of Divine truth was extinguished in all other places. The Lord has still taken care of his cause, while those who ought to have been serviceable thereto have lived and perished in their sins. The Son of David will still continue a light to his church, to establish it in truth and righteousness to the end of time. There are two kinds of fulfilling the law, one legal, the other by the gospel. Legal is, when men do all things required in the law, and that by themselves. None ever thus fulfilled the law but Christ, and Adam before his fall. The gospel manner of fulfilling the law is, to believe in Christ who fulfilled the law for us, and to endeavour in the whole man to obey God in all his precepts. And this is accepted of God, as to all those that are in Christ. Thus David and others are said to fulfil the law.