Jotham grew powerful because he walked steadfastly before the Lord his God.
NMVSo Toram [Yehovah is Perfect] became mighty, because he prepared his ways before the LORD-Yehōvah (Messiah Pre-Incarnate) his God-Elōhīm (The Living Word) [The Many Powered].
OJBSo Yotam became mighty, because he made the darkhei Yotam steadfast before Hashem Elohav.
T4TJotham faithfully obeyed Yahweh his God, and as a result he became a very powerful king.