John Gill Commentary Jeremiah 12:16

"And it shall come to pass, if they will diligently learn the ways of my people, to swear by my name, As Jehovah liveth; even as they taught my people to swear by Baal; then shall they be built up in the midst of my people." — Jeremiah 12:16 (ASV)

And it shall come to pass, if they will diligently learn the
ways of my people
Not their evil ways of sin or superstition, they sometimes stray into; but the ways which God has prescribed to them, and has directed them to walk in, and in which they do walk; and which are to be learned of the Lord, by a diligent attendance with his people on his word and ordinances; see (Isaiah 2:3) :

to swear by my name, the Lord liveth ;
that is, to worship and serve the living God, a self-existent Being, who has life in himself, and of himself, and not another; and is the fountain, author, and giver of natural life to all creatures, and spiritual and eternal life to his true worshippers: swearing is here put for the whole of religious worship, as in (Deuteronomy 6:13) :

(as they taught my people to swear by Baal; )
to worship him, and other idols:

then shall they be built in the midst of my people
become part of the spiritual building the church; being laid upon the same foundation of the apostles and prophets, and built up a holy temple; a spiritual house for the Lord to dwell in; partaking of the same privileges and ordinances as the people of God; being fellow heirs, and of the same body, and partakers of the promise in Christ by the Gospel, (Ephesians 2:20Ephesians 2:21) (3:6) , it denotes the settlement and establishment of the Gentiles with the Jews in a Gospel church state. So the Targum, ``and they shall be established in the midst of my people.''