Deuteronomy 4:21 (ESV)

21 Furthermore, the LORD was angry with me because of you, and he swore that I should not cross the Jordan, and that I should not enter the good land that the LORD your God is giving you for an inheritance.

By recalling once more (cf. Deuteronomy 1:37; Deuteronomy 3:26) that he was forbidden from entering the Promised Land, Moses emphasizes the importance of Israel exercising great caution. The Lord will not tolerate disobedience, no matter who commits it.