God made a statement to Israel that the Mekhilta reads as one of the most intimate promises in Scripture: "And you shall be unto Me." Not unto an angel. Not unto an intermediary. Unto Me directly. God declared: I am not setting up any others over you. I alone will be your guardian.
The proof text is (Psalms 121:4): "He will not slumber and He will not sleep, the Keeper of Israel." Other nations, according to rabbinic tradition, are assigned to the oversight of angelic princes — Michael for some, Gabriel for others. Each nation has its heavenly patron. But Israel has no intermediary. God Himself stands watch.
The implications are extraordinary. Every other nation's guardian can be distracted, overpowered, or overruled. Angels have limitations. They sleep. They falter. They can be defeated by other angels in the heavenly court. But Israel's guardian is God, who neither slumbers nor sleeps. The protection is absolute, continuous, and impossible to circumvent.
The Mekhilta is also explaining the unique vulnerability of Israel's position. Having no angelic intermediary means there is no buffer between Israel and God. When Israel sins, there is no angel to intercede, to soften the blow, to delay the consequence. The direct relationship cuts both ways — greater protection, but also greater accountability. God does not delegate Israel's punishment any more than He delegates Israel's protection.
"You shall be unto Me" is both a privilege and a burden. Israel belongs to God without middlemen, without proxies, without any created being standing in between. The Keeper of Israel keeps watch personally, and He never closes His eyes.