The Mekhilta extends its analysis of conditional versus unconditional covenants to two more foundational gifts: the Torah scroll and the priesthood of Aaron.
Whence is it derived that the Torah scroll was given unconditionally? From the verse (Deuteronomy 33:4): "The Torah which Moses commanded us is the eternal inheritance of the congregation of Jacob." The key word is "inheritance." An inheritance does not come with conditions attached. A father does not tell his son, "You may keep your inheritance if you behave well, but if you misbehave I will take it back." An inheritance, once given, belongs to the recipient permanently. By calling the Torah an inheritance of the congregation of Jacob, Scripture established that it belongs to the Jewish people forever — not as a loan, not as a conditional grant, but as an irrevocable possession.
The same unconditional permanence applies to the covenant with Aaron's priestly line. God declared (Numbers 18:19): "It is a covenant of salt forever." Salt preserves. Salt does not decay. A covenant of salt is one designed to last without deterioration. And the Torah reinforces this with a second verse (Numbers 25:13): "And it shall be unto him and to his seed after him a covenant of eternal priesthood."
Two gifts, both unconditional. The Torah belongs to all of Israel without conditions, and the priesthood belongs to Aaron's descendants without conditions. Neither can be revoked, neither can expire, and neither depends on the worthiness of the recipients.