Bible Dictionary
ENGAGE
To pledge, become surety, or commit oneself. In Jeremiah 30:21 the expression concerns one who has shown boldness or pledged himself.
Biblical Usage
Jeremiah 30:21 asks, in the King James Version, who has “engaged his heart.” The Revised Version renders the expression “he that hath had boldness,” with a marginal explanation, “hath been surety for his heart.”