John Gill Commentary Deuteronomy 28:13

"And Jehovah will make thee the head, and not the tail; and thou shalt be above only, and thou shalt not be beneath; if thou shalt hearken unto the commandments of Jehovah thy God, which I command thee this day, to observe and to do [them]," — Deuteronomy 28:13 (ASV)

And the Lord shall make you the head, and not the tail. Give them dominion over others, and not make them subject to them; the head signifies rulers and governors, and the tail the common people that are subjects; or the one such that are honourable and in high esteem, and the other such that are mean and base; see (Isaiah 9:14Isaiah 9:15) ; the Targum of Jonathan is, ``the Word of the Lord shall make you''

and you shall be above only, and you shall not be beneath. Which explains what is meant by head and tail, being uppermost and lowermost, as the head is the upper part, and the tail the lower part of a creature; the one is more honourable, the other vile:

The sense is, that they should be superior to other people in honour and dignity, and not below them, or vassals to them:

if that you hearken to the commandments of the Lord your God, which I command you this day to observe and to do [them]. Which is the condition on which all this happiness depended.