Unfortunately, both are referred to as "Passover" and its up to us to sleuth out the distinction.
In this case, the OT reveals the NT.
Back to the Beginning
Leviticus 23: “These are the feasts of the Lord, even holy convocations,
which ye shall proclaim in their seasons.
In the fourteenth day of the first month at even is the Lord’s passover” (verses 4-5).
Notice first that this is God’s Passover—not the Jews’—and the day it is to be kept
is the 14th, not the 15th.
the days are to begin and end at even, or sunset (see Lev 23:32; Deut 16:6; Psalm 104:19).
the Passover begins at sunset, at the beginning of the 14th.
The Jewish community observes their Passover on the 15th beginning at sunset.
Leviticus 23:6 tells us that the first day of Unleavened Bread is on the 15th.
the Passover and the Days of Unleavened Bread are different and separate festivals.
Before covering the events of the Passover in the New Testament,
let’s first review the events as they occurred in the Old Testament.
-Between the Two Evenings
First of all, the Passover lamb was to be sacrificed “in the evening” (Exodus 12:6)
on the 14th day of the first month. “In the evening” is between sunset and dark.
Deuteronomy 16:6 confirms this when it says the lamb was sacrificed “at even,
at the going down of the sun.” “the time between sunset and deep twilight.”
Exodus 12:8 says the Israelites were to eat the Passover meal “in that night.” Which night?
The one mentioned in verse 6: the 14th. After that, God smote the firstborn “this night”
(verse 12). Not the next night—this night—the 14th!
That is why, in Numbers 28:16, it says, “And in the fourteenth day of the first month is
[the passover of the Lord]” (we see also Leviticus 23:5-6).
5In the fourteenth day of the first month at even is [the Lord's passover].
6And on the fifteenth day of the same month is the feast of unleavened bread
unto the Lord: seven days ye must eat unleavened bread.
The events of the Passover occur in the 14th. And the events of
the first day of Unleavened Bread occur in the 15th!
Exodus 12:21-22 the Israelites were not to leave their houses until morning.
If they did, they would have died. This is why they were to burn their leftovers
the next morning (verse 10).the morning after the Passover is still the 14th
—the day portion of the 14th.
(verse 11)
11And thus shall ye eat it; with your loins girded, your shoes on your feet,
and your staff in your hand; and ye shall eat it in haste: it is [the Lord's passover].
-
Deuteronomy 16:1 says they left Egypt “by night.” Their exodus from Egypt
then had to be that following night, or the night[start] of the 15th.
This was to be a “night to be much observed” (Exodus 12:42).
This is confirmed in Numbers 33:3: “And they departed … on the fifteenth day
of the first month; on the morrow AFTER the passover .…”
the spoiling of the Egyptians (Exodus 12:33-36). This could have only taken place on the
afternoon of the 14th, just hours before [the Israelites left Egypt the night of the 15th].
-
How did the Passover get its name originally? “For the Lord will pass through to smite
the Egyptians; and when he seeth the blood upon the lintel, and on the two side posts,
the Lord will pass over the door, and will not suffer the destroyer to come in unto your
houses to smite you. … That ye shall say, It is the sacrifice of the Lord’s passover, who
passed over the houses of the children of Israel in Egypt, when he smote the Egyptians,
and delivered our houses. And the people bowed the head and worshipped” (Exodus 12:23, 27).
God passed over the houses that had the blood of the lamb on their doorpost.
God also passes over (forgives) our sins when we repent of them and come
under the shed blood of Jesus Christ our Passover, sacrificed for us.
Kept on the 14th Many Generations Later
When the Hebrew children would ask about this service years later, the parents were to
respond, “It is the sacrifice of the Lord’s Passover” (Exodus 12:27). this is God’s Passover,
and God said “the fourteenth day of the first month at even is the Lord’s passover” (Lev 23:5).
Many generations later, the Israelites were still keeping the Passover on the 14th.
They kept the Passover on the correct day when they were in the wilderness (Numbers 9:5).
When they entered into the Promised Land, they were still all in agreement (Joshua 5:10).
King Josiah kept the Passover on the 14th (2 Chronicles 35:1). We also read in Ezra’s time
they were still keeping it on the 14th (Ezra 6:19), and this was about 519 b.c.
But the New Testament Jews Keep it a Day Later
the Jews were not all keeping the same day as Jesus Christ did and commanded.
“And the Jews’ passover was at hand, and Jesus went up to Jerusalem” (John 2:13).
Here it is called “the Jews’ Passover”—not “the Lord’s Passover.”
The Jewish confusion most likely arose in the third century before Christ.
The Palestinian Jews were under Egyptian control from 301 to 198 b.c.
“While the Egyptians allowed the Jews to retain their ancient calendar, there was a
change made in the beginning of the day—it became common to begin the day at sunrise.
This custom was adopted, and persisted among the Jews even down to New Testament times