Jamieson, Fausset and Brown on Jeremiah 17:3

3. mountain--Jerusalem, and especially Zion and the temple.

in the field--As Jerusalem was surrounded by mountains (Psa 125:2), the sense probably is, Ye rely on your mountainous position (Jr 3:23), but I will make "My mountain" to become as if it were in a plain (field), so as to give thy substance an easy prey to the enemy [Calvin]. "Field" may, however, mean all Judea; it and "My mountain" will thus express the country and its capital. (Gesenius translates, "together with," instead of "in"; as the Hebrew is translated in Jr 11:19; Ho 5:6; but this is not absolutely needed), "the substance" of both of which God "will give to the spoil."

thy high places--corresponding in parallelism to "My mountain" (compare Is 11:9), as "all thy borders," to "the field" (which confirms the view that "field" means all Judea).

for sin--connected with high places" in English Version, namely, frequented for sin, that is, for idolatrous sacrifices. But Jr 15:13 makes the rendering probable, "I will give thy substance ... to ... spoil ... on account of thy sin throughout all thy borders."