Exodus 34:25
Thou shalt not offer the blood of my sacrifice with leaven; neither shall the sacrifice of the feast of the passover be left unto the morning. Thou shalt not offer the blood of my sacrifice with leaven; neither shall the sacrifice of the feast of the passover be left unto the morning.
Exodus 34:25 belongs to the covenant words given during Moses's forty days and nights in the mount. Miraculously sustained and alone with God, he presented two tables of stone that he had prepared, and God wrote upon them the words of the covenant, the Ten Commandments. Afterward Moses descended with his face reflecting the glory of the divine presence with a dazzling light that guilty Israel could not endure. Aaron and the people were afraid to come near, and Moses put a veil upon his face whenever he returned to the camp from communion with God.
The verse is part of the statement of what God requires of His people. It shows that God specifies exactly what He wants, so it matters what day is kept and carelessness and indifference about it are without excuse. The very day specified by God is the seventh day, leaving no excuse for keeping the first day of the week.