מדרש על מכות 45:13

I might think, (that they were steeped in blood) even after they received it; it is, therefore, written "only" (a term of limitation). Once they received it, they observed it with joy. [Rabban Gamliel says: It states "Only strengthen yourself not to eat the blood". If Scripture exhorted us so concerning the "lightest" mitzvah of the Torah, (not to eat) blood, how much more so are we thus exhorted concerning the other mitzvoth of the Torah!]

(Rabban Gamliel says: It states "Only strengthen yourself not to eat the blood". If Scripture exhorted us so concerning the "lightest" mitzvah of the Torah, (not to eat) blood, how much more so are we thus exhorted concerning the other mitzvoth of the Torah!)