Charles Spurgeon Commentary Jeremiah 3:22-23

"Return, ye backsliding children, I will heal your backslidings. Behold, we are come unto thee; for thou art Jehovah our God. Truly in vain is [the help that is looked for] from the hills, the tumult on the mountains: truly in Jehovah our God is the salvation of Israel." — Jeremiah 3:22-23 (ASV)

Behold, we come unto you, for you are the LORD our God.

Truly in vain is salvation hoped for from the hills, and from the multitude of mountains:

We leave all false confidences. We forsake our earthly joys.

Return, you backsliding children, and I will heal your backslidings. Behold, we come to you; for you are the LORD our God. Truly in vain is salvation hoped for from the hills, and from the multitude of mountains: truly in the LORD our God is the salvation of Israel.

So they come back to him, and find the salvation which they need.