John Gill Commentary Jeremiah 12:2

"Thou hast planted them, yea, they have taken root; they grow, yea, they bring forth fruit: thou art near in their mouth, and far from their heart." — Jeremiah 12:2 (ASV)

You have planted them
In the land of Canaan, fixed the bounds of their habitation, given them a firm and comfortable settlement; for all the good things, even of the wicked, come from God:

yes, they have taken root ;
as everything that is planted does not; but these did, though it was downwards in the earth, on which their hearts were set, and so were strengthened and established in their worldly circumstances:

they grow, yes, they bring forth fruit ;
but to themselves, not to God; not fruits of righteousness or good works; they grow, not in grace and holiness, but in their worldly substance; and they brought forth fruit, not such as were meet for repentance, but they had great riches, and numerous families; and so the Septuagint and Arabic versions, "they produce children, and bring forth fruit." The Targum is, ``they become rich, yes, they possess substance.''

You are near in their mouth ;
they often made use of the name of God, either in swearing by it, or praying to him in an external manner; they called themselves the Lord's people, and boasted of being his priests, and employed in his service; they took his covenant, and the words of your law, into their mouths, and taught them the people, and yet had no sincere regard for these things:

and far from their reins ;
from the affections of their hearts, and the desires of their souls; they had no true love for God, nor fear of him, nor faith in him. The Targum is, ``near are the words of your law in their mouth, and far is your fear from your reins.''