Whoever will not give heed to my words which he shall speak in my name: Contemporary English Version expresses the sense better with “Since the message comes from me, anyone who doesn’t obey the message will….”

I myself will require it of him: see similar statements in Gen 9.5; Ezek 33.6; 34.10. It means that God will hold that person responsible. New Jerusalem Bible has “will have to render an account to me,” New Jewish Publication Society’s Tanakh “I myself will call him to account,” and Revised English Bible “I shall call that person to account.” This “calling to account,” of course, means punishment (see Good News Translation).

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on Deuteronomy. (UBS Helps for Translators). New York: UBS, 2000. For this and other handbooks for translators see here .