פּירוש אויף דברים 6:13

ובשמו תשבע AND THOU SHALT SWEAR BY HIS NAME — If thou hast all the characteristics mentioned here, i.e. that thou reverest His name and servest Him, then thou mayest take an oath by mention of His name, for just because thou reverest His name, thou wilt be cautious with thy oath; but if not, thou shalt not so swear.

ובשמו תשבע, “and (only) in His name may you pronounce any oaths.” Make sure that when you do swear, that everyone who hears you knows that you are using only His name. When others make you take an oath, do not violate that oath, as you have sworn in His name.

THOU SHALT FEAR THE ETERNAL THY G-D. The purport thereof is that after he commanded concerning the love of G-d, he mentioned that [one is] to fear Him so that he not sin and be punished.