Charles Ellicott Commentary Deuteronomy 4:21-23

"Furthermore Jehovah was angry with me for your sakes, and sware that I should not go over the Jordan, and that I should not go in unto that good land, which Jehovah thy God giveth thee for an inheritance: but I must die in this land, I must not go over the Jordan; but ye shall go over, and possess that good land. 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 4:21-23 (ASV)

The Lord was angry with me for your sakes ... I must die in this land ... but ye shall go over ... Take heed unto yourselves. —The argument appears to be this: “I cannot go with you to warn you; therefore take more heed when you are alone.” The same line of thought appears in St. Paul’s last appeal to Timothy: Fulfil thy ministry; for I am now ready to be offered (2 Timothy 4:6).