A New Worship Theme

As Easter replaced Passover, not only was a new date selected (the Sunday after the spring equinox rather than the biblically directed (Nisan 14), (the Jewish calendar in ancient Hebrew) a new theme was introduced. Rather than commemorating Christ's death as directed by the Scriptures. 1 Corinthians (11:26). For every time you eat this bread and drink this cup, you are representing and signifying and proclaiming the fact of the Lord's death until He comes again.

See, the new holiday was designed to celebrate His resurrection. This new theme easily accommodated the pagan fertility symbols. It also helped distinguish the Christian community from the Jews, a major goal of church leaders of the time.

Although Christ's resurrection is an important basis of our hope that we, too, can be resurrected, 1 Corinthians (15:17). And if Christ be not raised, your faith is vain; ye are yet in your sins.
See, Romans (5:10). For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life.
And it was critical for God's plan of salvation to continue, neither God the Father, Christ nor Scripture has ever explicitly directed us to celebrate this event.

Indeed, the love of God is primarily expressed to all humanity through the crucifixion of Jesus Christ John (3:16).For God so loved the world, that he gave his only begotten Son, that whosoever believes in him shall not perish, but have everlasting life.

Hebrews (9:28). So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.
His death, through which our sins may be forgiven, is the primary focus of the Passover, not His resurrection. Many precise details of His death and events leading up to and encompassing it were prophesied in the Hebrew Scriptures hundreds of years in advance.

The decision of God the Father to willingly give His only begotten Son--and of Jesus Christ to surrender His life to torture and execution as a sacrifice for the sins of humanity--were far more demanding than the demonstration of God's power over death through the resurrection.

Mankind's need for a Savoir

There is more to consider. The Bible discusses sin and our need for forgiveness and reconciliation to God (the theme of the biblically commanded Passover and the Days of Unleavened Bread) far more often than the subject of the resurrection. The word sin is used 447 times compared with the word resurrection being used only 41 times. Don't forget that sin was the cause of Christ's death. Only by repenting of our sins and being reconciled to God by the death of Christ can we be assured of being resurrected. Acts (2:38).Then Peter said unto them, Repent, and be baptised every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. John (5:29) And shall come forth; they that have done good, unto the resurrection of life; and they that have done evil, unto the resurrection of damnation. John (11:25). Jesus said unto her, I am the resurrection, and the life: he that believes in me, though he were dead, yet shall he live:

This is not to minimize the importance of Christ's resurrection. It, too, is a crucial step in the salvation process 1 Corinthians (15). After being reconciled to God the Father by the death of His Son, ultimately we are saved by Christ's life as He pleads for us in the role of our High Priest and lives in us through the Holy Spirit, helping us to overcome sin. Romans (5:10). For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life.

Hebrews (4:14-16).  Seeing then that we have a great high priest, that is passed into the heavens, Jesus the Son of God, let us hold fast our profession.
For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin.
Let us therefore come boldly unto the throne of grace, that we may obtain mercy, and find grace to help in time of need.

1 John (2:1). My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
See, Galatians (2:20). I am crucified with Christ: nevertheless I live; yet not I, but Christ lives in me: and the life which I now live in the flesh I live by the faith of the son of God, who loved me, and gave himself for me.
The process of our coming out of sin is pictured in the biblical feast immediately following Passover, the Days of Unleavened Bread, during which Christ's resurrection occurred.

Again, though, the Bible nowhere instructs Christians to keep a special celebration of Christ's resurrection, nor is there a biblical record of early Christians doing so. But it is clear that both Jesus Christ and the apostle Paul expected Christ's followers to commemorate His sacrificial death on our behalf in a special ceremony. Matthew (26:26-28).And as they were eating, Jesus took bread, and blessed it, and broke it , and gave it to the disciples, and said, Take, eat; this is my body.
And he took the cup, and gave thanks, and gave it to them, saying, Drink ye all of it;
For this is my blood of the new testament, which is shed for many for the remission of sins. 1 Corinthians (5:7). Purge out therefore the old leaven, that you may be a new loaf, as you are unleavened. For even Christ our passover is sacrificed for us:

Nonetheless, the celebration of Easter prevailed. Those who remained faithful to Christ's example of keeping the Passover and the Days of Unleavened Bread decreased in number and were persecuted by those favouring Easter.

Vine's Complete Expository Dictionary of Old and New Testament Words says about the term Easter here: "Pascha, mistranslated ‘Easter' in Acts (12:4). And when he had apprehended him, he put him in prison, and delivered him to four quaternions of soldiers to keep him; intending after Easter to bring him forth to the people.

KJV, denotes the Passover.The term ‘Easter' is not of Christian origin. It is another form of Astarte, one of the titles of the Chaldean goddess, the queen of heaven. The festival of Pasch  [Passover] held by Christians in post-apostolic times was a continuation of the Jewish feast. From this Pasch the pagan festival of ‘Easter' was quite distinct and was introduced into the apostate Western religion, as part of the attempt to adapt pagan festivals to Christianity". "Easter"). 
Scriptures are from the (N.I.V)
And (K.J.V)