John Gill Commentary Deuteronomy 4:23

"Take heed unto yourselves, lest ye forget the covenant of Jehovah your God, which he made with you, and make you a graven image in the form of anything which Jehovah thy God hath forbidden thee." — Deuteronomy 4:23 (ASV)

Take heed unto yourselves
Since he should not be long with them, to advise, instruct, and caution them:

lest you forget the covenant of the Lord your God ,
which he made with you; what that required of them, and what was promised unto them on the performance of it, and what they must expect should they break it, and particularly be so forgetful of it, and the first articles in it, as follows:

and make you a graven image, or the likeness of anything which the
Lord your God has forbidden you ;
a graven image in the likeness of men or women, of any beast on the earth, or fowl in heaven, or fish in the sea.