John Gill Commentary Jeremiah 17:3

"O my mountain in the field, I will give thy substance and all thy treasures for a spoil, [and] thy high places, because of sin, throughout all thy borders." — Jeremiah 17:3 (ASV)

O my mountain in the midst of the field
Meaning either the temple, called the mountain of the house, and of the Lord's house, (Micah 3:12) (4:1), or else Jerusalem, which stood on a hill in the midst of a plain, surrounded with fruitful fields and gardens; or in the midst of a land like a field. The Targum is, "because you worship idols upon the mountains in the field:"

I will give your substance and all your treasures to the spoil; all the riches of the city and temple to be the spoil and plunder of the enemy; (See Gill on Jeremiah 15:13).

and your high places for sin, throughout all your borders. The sense is, that all their substance and treasure throughout their borders, the riches of the whole land, as well as of the city and temple, (Jeremiah 15:13) and all their high places throughout the land, which were used for sin, for idolatrous practices, on account thereof, should become the spoil of the enemy.