The Geneva Bible Translation Notes, [1599], at sacred-texts.com
(a) That is, to offer incense against the word of God, which is spoken of in the commendation of Jotham.
(b) They were not completely purged from idolatry.
He built the high (c) gate of the house of the LORD, and on the wall of Ophel he built much.
(c) Which was 60 cubits high and was for the height called Ophel: it was at the east gate and mention is made of it in (Ch2 3:4).
So Jotham became mighty, (d) because he prepared his ways before the LORD his God.
(d) He shows that all prosperity comes from God, who never fails when we put our trust in him.