Exodus 18 · a question people ask
Did Jethro already worship the LORD, or did he come to know him here?
The chapter records what Jethro said and did. He "rejoiced for all the goodness which the LORD had done to Israel" (18:9), said, "Blessed be the LORD" (18:10) and "Now I know that the LORD is greater than all gods" (18:11), and took "a burnt offering and sacrifices for God"; Aaron and all the elders of Israel came "to eat bread with Moses’ father-in-law before God" (18:12). It doesn't say what Jethro believed before. Christians read it in two main ways. Both agree that the chapter shows a priest of Midian blessing the LORD for what he did for Israel.
How Christians read it
Where Christians differ, Favor sets out the main views side by side and doesn't pick one.
He came to know the LORD here
Those who hold this view point to "Now I know" (18:11), which Jethro says after hearing of "all that God had done" (18:1) and all that Moses told him (18:8). They read his words as a priest of Midian coming to know the LORD through what the LORD had done for Israel.
Exodus 18:1 · Exodus 18:8-11
He already worshiped God
Those who hold this view note that Midian was a son of Abraham (Genesis 25:1-2), that Jethro speaks of God freely, "I will give you counsel, and God be with you" (18:19), and that he takes "a burnt offering and sacrifices for God", and Aaron and all the elders come "to eat bread with Moses’ father-in-law before God" (18:12). They read "Now I know" as a worshiper of God seeing that the LORD is greater than all gods, not as the first time he knew him.
Genesis 25:1-2 · Exodus 18:12 · Exodus 18:19
The verses
“Now Jethro, the priest of Midian, Moses’ father-in-law, heard of all that God had done for Moses and for Israel his people, how the LORD had brought Israel out of Egypt.”