Exodus 23:18-19

"Thou shalt not offer the blood of my sacrifice with leavened breads; neither shall the fat of my feast remain all night until morning. The first of the first-fruits of thy ground thou shalt bring into the house of Jehovah thy God, Thou shalt not boil a kid in its mother's milk."

That the Passover itself was clearly in view in the previous verse is proved by the mention here of one of the key regulations of that feast, namely, that all of it should be consumed, before morning.

"Thou shalt not boil a kid in its mother's milk ..." Rawlinson assigned this reason for this prohibition: "Feeling revolts from it, and the general sense of civilized mankind re-echoes the precept."[17] The mixing of meat and milk dishes is in no circumstance considered `Kosher' by the Jews their custom being founded partially upon this verse. "They even keep separate kitchens for the preparation of milk and meat dishes."[18]

The most probable reason, it seems, for this prohibition lay in the pagan use of "a kid boiled in its mother's milk" as a magical formula for increasing the fertility of the land! "Milk so boiled was sprinkled on the crops. The pagan idea was that the new life of the kid added to its mother's milk produced double fertility."[19] This prohibition seemed at such variance with other Divine commandments that for generations men simply could not understand the reason for it; as Rawlinson said, "Reason has nothing to say against such a mode of preparing food."[20] However, the mystery was unlocked in the 1930, when the reason for this pagan practice was discovered in Ugaritic literature.[21] With this information, it is easy to understand why God would not allow Israel to do anything resembling the pagan rites of idolatrous nations around them.

Two other things in these passages should be noted. The command not to come "empty" before God (Exodus 23:15) established giving as an essential and normal part of the worship of God, a principle that is brought over into Christianity and made binding upon all believers.

The prohibition that leavened bread should not be offered with the blood of the sacrifice was repudiated by the religious apostasy in Northern Israel. Amos 4:5 mentioned among the sins of Israel the offering of a sacrifice with leavened bread, the significance of this being that these Pentateuchal regulations were familiar to Israel for long centuries prior to the dates some critics would like to affix to the Pentateuch. Amos' mention of such a perversion of God's worship also proved that it was not social issues alone that formed the burden of Israel's apostasy. See extensive notes on these issues in Volume 1 of my commentary on the minor prophets.