Matthew Henry Commentary 1 Kings 15:1-8

"Now in the eighteenth year of king Jeroboam the son of Nebat began Abijam to reign over Judah. Three years reigned he in Jerusalem: and his mother`s name was Maacah the daughter of Abishalom. And he walked in all the sins of his father, which he had done before him; and his heart was not perfect with Jehovah his God, as the heart of David his father. Nevertheless for David`s sake did Jehovah his God give him a lamp in Jerusalem, to set up his son after him, and to establish Jerusalem; because David did that which was right in the eyes of Jehovah, and turned not aside from anything that he commanded him all the days of his life, save only in the matter of Uriah the Hittite. Now there was war between Rehoboam and Jeroboam all the days of his life. And the rest of the acts of Abijam, and all that he did, are they not written in the book of the chronicles of the kings of Judah? And there was war between Abijam and Jeroboam. And Abijam slept with his fathers; and they buried him in the city of David: and Asa his son reigned in his stead." — 1 Kings 15:1-8 (ASV)

Abijam's heart was not perfect with the Lord his God; he lacked sincerity; he began well, but he fell away and walked in all the sins of his father, following his bad example, even though he had seen its bad consequences. David's family 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 continually taken care of his cause, while those who ought to have been serviceable to it have lived and perished in their sins. The Son of David will still continue as 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 fulfillment is when people do all things required in the law, and do so by their own power. No one ever fulfilled the law in this way except 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 strive with their whole being to obey God in all his precepts. And this is accepted by God from all those who are in Christ. In this way, David and others are said to fulfill the law.