Albert Barnes Commentary Jeremiah 2:3

"Israel [was] holiness unto Jehovah, the first-fruits of his increase: all that devour him shall be held guilty; evil shall come upon them, saith Jehovah." — Jeremiah 2:3 (ASV)

Meaning: “Israel” is an offering consecrated to Yahweh, His firstfruits of increase. The firstfruits were God’s consecrated property, His portion of the whole harvest.

Pagan, that is, unconsecrated, nations must not meddle with Israel, because it is the nation consecrated to God. If they do, they will bring such guilt upon themselves as those incur who eat the firstfruits (Leviticus 22:10, Leviticus 22:16).