The chief priests, the scribes, and the principal men could not stand Jesus' actions and public teaching. On Nisan the 11th they had questioned Jesus on whose authority he did all those things.(Matthew 21:23-27)
The last day of Jesus' public ministry before his arrest, trial, and execution Jesus discussed several aspects of 'the sign of his presence.' He emphasized the need to "keep on the watch." Why? "Because, you do not know on what day your Lord is coming." (Luke 21:5, 6; Matthew 24:3, 42; Mark 13:3, 4, 7, 14, 21, 33, 35, 37; Luke 21:10, 11)
Jesus spended Nisan 12 quietly with his disciples. He realized that the religious leaders desperately wanted to kill him, and he did not want them to hinder his Passover celebration the following evening. (Mark 14:1, 2)
On Nisan 13, people were busy making final arrangements for the Passover. Early in the afternoon, Jesus had send Peter and John to prepare the Passover for them in an upper room in Jerusalem. (Mark 14:12-16; Luke 22:8) A little before sundown, Jesus and the other ten apostles met them there for their last Passover celebration.
“and he said to them, “I have really wanted so much to celebrate this Seder with you before I die! for I tell you, it is certain that I will not celebrate it again until it is given its full meaning in the kingdom of god.”” (Luke 22:15-16 CJB)
“also, taking a piece of matzah, he made the b’rakhah, broke it, gave it to them and said, “this is my body, which is being given for you; do this in memory of me.” he did the same with the cup after the meal, saying, “this cup is the new covenant, ratified by my blood, which is being poured out for you.” (Luke 22:19-20 CJB)
“while they were eating, Yeshua took a piece of matzah, made the b’rakhah, broke it, gave it to the talmidim and said, “take! eat! this is my body!” also he took a cup of wine, made the b’rakhah, and gave it to them, saying, “all of you, drink from it! for this is my blood, which ratifies the new covenant, my blood shed on behalf of many, so that they may have their sins forgiven.” (Matthew 26:26-28 CJB)
Reason For ObservanceLuke 22:19, 20 Also, he took a loaf, gave thanks, broke it, and gave it to them, saying: "This means my body which is to be given in YOUR behalf. Keep doing this in remembrance of me." 20 Also, the cup in the same way after they had the evening meal, he saying: "This cup means the new covenant by virtue of my blood, which is to be poured out in YOUR behalf.
1 Corinthians 11:20, 26 Therefore, when YOU come together to one place, it is not possible to eat the Lord's evening meal. 26 For as often as YOU eat this loaf and drink this cup, YOU keep proclaiming the death of the Lord, until he arrives.
Romans 6:23 For the wages sin pays is death, but the gift God gives is everlasting life by Christ Jesus our Lord
Exodus 12:26,27 26 And it must occur that when YOUR sons say to YOU, 'What does this service mean to YOU?' 27 then YOU must say, 'It is the sacrifice of the passover to Jehovah, who passed over the houses of the sons of Israel in Egypt when he plagued the Egyptians, but he delivered our houses.'" Then the people bowed low and prostrated themselves.
In obedience to Christ's instructions, "Keep doing this in remembrance of me," the 14th day of Nisan should be continued to be observed by his followers till this day as the time for memorializing Christ's death. (Luke 22:19, 20)