The content of verses 5-20 is unique to the book of 2 Chronicles. This information is not found in the parallel text of 2 Kings.
He set himself to seek God in the days of Zechariah: To seek God is a common expression in 1-2 Chronicles (see the comments on 1 Chr 16.10 and 2 Chr 11.16). Here it means “to serve God” or “to follow God’s will.” New Century Version begins this verse with “Uzziah obeyed God….” At least thirty different men in the Old Testament have the name Zechariah. Whether this Zechariah is to be identified with the Zechariah mentioned in Isa 8.2 or with Zechariah, the son of Jehoiada (2 Chr 24.20), is uncertain. But the latter seems more probable.
Who instructed him in the fear of God: The Hebrew text does not have the object pronoun him. But many languages will require an object, and what is implied is that Zechariah instructed or taught Uzziah. In the fear of God is perhaps an allusion to the Hebrew Scriptures (see the comments on 2 Chr 19.7). Good News Translation loosely translates this whole clause as “his religious adviser.” Instead of in the fear of God, which follows some Hebrew manuscripts, the Masoretic Text has “in seeing God.” Critique Textuelle de l’Ancien Testament gives a {B} rating to this second reading, and it is followed by a number of modern versions, which have “through the vision of God” (NASB) or “in the visions of God” (New Jewish Publication Society’s Tanakh; similarly Complete Jewish Bible, Nouvelle Bible Segond). Bible en français courant follows this reading also and renders the whole clause as “who was able to understand the visions sent by God.”
And as long as he sought the LORD: The Hebrew text here is not clear. According to the Revised Standard Version rendering, the Hebrew word translated and as long as refers to the period of time that Uzziah sought to serve God. It is also possible that this word refers to the period of time that Zechariah lived. Bible en français courant follows this interpretation by rendering the whole verse as “As long as Zechariah lived, who was able to understand the visions sent by God, Uzziah sought to know the will of the Lord God, and it made him successful.”
God made him prosper: This clause may refer to Uzziah’s positive relationships with neighboring nations. Moffatt says “God gave him success,” and Contemporary English Version has “God made him successful.” Another possible model is “God caused him to prosper.”
Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on 1-2 Chronicles, Volume 1. (UBS Helps for Translators). Miami: UBS, 2014. For this and other handbooks for translators see here .