The 14th day of the month of Nisan (see Bible Months) is one of the most important dates of all Bible History. It marked the time of Passover from which the Israelites began their Exodus from Egypt, and centuries later, the time of the sacrifice of Jesus Christ, the "Lamb of God." The early Christian church continued to observe Passover, on the 14th of Nisan, as Jesus Christ did Himself all through His life, until the Roman festival of Easter (of which many Christians today are often shocked to learn was named after the Babylonian idol Ishtar, and later, eastre, the Anglo-Saxon goddess of light, or spring) was officially enforced upon the Christian-professing world by the Roman Empire (see Ancient Empires - Rome). The Easter of Acts 12:4 in the otherwise excellent King James Version should have been translated as Passover (as most other translations do), since that is the word, and the intended observance, that was originally written in the Scriptures.
Passover In Egypt
Passover was instituted by The Lord as a foreshadow of the ultimate Lamb of God. A lamb "without blemish" (see below) was chosen to symbolize the sinless Messiah.
"And Moses said, "Thus says The Lord [see Rock Of Ages]: About midnight I will go forth in the midst of Egypt; and all the first-born in the land of Egypt shall die, from the first-born of Pharaoh [see Who Was The Exodus Pharaoh?] who sits upon his throne, even to the first-born of the maidservant who is behind the mill; and all the first-born of the cattle. And there shall be a great cry throughout all the land of Egypt, such as there has never been, nor ever shall be again. But against any of the people of Israel, either man or beast, not a dog shall growl; that you may know that The Lord makes a distinction between the Egyptians and Israel. And all these your servants shall come down to me, and bow down to me, saying, 'Get you out, and all the people who follow you.' And after that I will go out." And he went out from Pharaoh in hot anger."
"Then The Lord said to Moses, "Pharaoh will not listen to you; that My wonders may be multiplied in the land of Egypt" [see The Ten Plagues]. Moses and Aaron did all these wonders before Pharaoh; and The Lord hardened Pharaoh's heart, and he did not let the people of Israel go out of his land." (Exodus 11:4-10 RSV)
"The Lord said to Moses and Aaron in the land of Egypt, "This month shall be for you the beginning of months; it shall be the first month of the year for you [see Bible Calendar]. Tell all the congregation of Israel that on the tenth day of this month they shall take every man a lamb according to their fathers' houses, a lamb for a household; and if the household is too small for a lamb, then a man and his neighbor next to his house shall take according to the number of persons; according to what each can eat you shall make your count for the lamb."
"Your lamb shall be without blemish, a male a year old; you shall take it from the sheep or from the goats; and you shall keep it until the fourteenth day of this month, when the whole assembly of the congregation of Israel shall kill their lambs in the evening. Then they shall take some of the blood, and put it on the two doorposts and the lintel of the houses in which they eat them. They shall eat the flesh that night, roasted; with unleavened bread and bitter herbs they shall eat it. Do not eat any of it raw or boiled with water, but roasted, its head with its legs and its inner parts."
"And you shall let none of it remain until the morning, anything that remains until the morning you shall burn. In this manner you shall eat it: your loins girded, your sandals on your feet, and your staff in your hand; and you shall eat it in haste. It is The Lord's Passover."
"For I will pass through the land of Egypt that night, and I will smite all the first-born in the land of Egypt, both man and beast; and on all the gods of Egypt I will execute judgments: I am The Lord. The blood shall be a sign for you, upon the houses where you are; and when I see the blood, I will pass over you, and no plague shall fall upon you to destroy you, when I smite the land of Egypt. "This day shall be for you a memorial day, and you shall keep it as a feast to The Lord; throughout your generations you shall observe it as an ordinance for ever." (Exodus 12:1-14 RSV)
Jesus Christ observed the Passover because He was the Passover.
"Behold, the Lamb of God, who takes away the sin of the world!" (John 1:29 RSV)
"Worthy art thou to take the scroll and to open its seals, for thou wast slain and by Thy blood didst ransom men for God from every tribe and tongue and people and nation" (Revelation 5:9 RSV)
Fact Finder: How did Jesus Christ, by His own example that night, instruct Christians in how to observe Passover?
Matthew 26:26-28, Mark 14:22-24, Luke 22:14-20, John 13:1-17