The resurrection gives us tangible proof that Christianity is true Life versus another religion or philosophy!
It is written by The Holy Spirit in Acts chapter 1:
1 The former account I made, O Theophilus, of all that Jesus began both to do and teach,
2 until the day in which He was taken up, after He through the Holy Spirit had given commandments to the apostles whom He had chosen,
3 to whom He also presented Himself alive after His suffering by many infallible proofs, being seen by them during forty days and speaking of the things pertaining to the Kingdom of God.
What was the purpose of Jesus teaching the apostles for forty days after His resurrection? Jesus had to present the revelation of the cross and resurrection because the disciples’ mindset needed to be changed. They were no longer to be under the Old Covenant and its sacrifices.
Before the cross, GOD was with us. After the resurrection, GOD could and would operate in us. Jesus told them to wait for the Promise of The FATHER… The Holy Spirit.
Jesus had spoken to them concerning The Holy Spirit in John chapter 14:
15 “Loving me empowers you to obey My commands.
16-17 And I will ask the Father and He will give you another Savior, the Holy Spirit of Truth, who will be to you a friend just like me—and He will never leave you. The world won’t receive Him because they can’t see Him or know Him. But you will know Him intimately, because He will make His home in you and will live inside you.
Until Jesus fulfilled our sin issue once and for all, The Holy Spirit could not live inside us for we were unrighteous. Righteousness could not reside with unrighteousness.
Paul wrote of this revelation by The Holy Spirit in Romans chapter 6:
5 For if we have been united together in the likeness of His death, certainly we also shall be in the likeness of His resurrection,
6 knowing this, that our old man was crucified with Him, that the body of sin might be done away with, that we should no longer be slaves of sin.
7 For he who has died has been freed from sin.
8 Now if we died with Christ, we believe that we shall also live with Him,
9 knowing that Christ, having been raised from the dead, dies no more. Death no longer has dominion over Him.
10 For the death that He died, He died to sin once for all; but the life that He lives, He lives to God.
11 Likewise you also, reckon yourselves to be dead indeed to sin, but alive to God in Christ Jesus our Lord.
Paul also wrote by The Holy Spirit in 2nd Corinthians chapter 5:
17 Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new.
18 Now all things are of God, who has reconciled us to Himself through Jesus Christ, and has given us the ministry of reconciliation,
19 that is, that God was in Christ reconciling the world to Himself, not imputing their trespasses to them, and has committed to us the Word of reconciliation.
In other words, it was through Jesus, the Anointed One, that God was shepherding the world, not even keeping records of their transgressions, and He has entrusted to us the ministry of opening the door of reconciliation to God.
It was vital the disciples understood the transition from the Old Covenant to the New. Their mindset had to be changed so they could teach this new revelation that when salvation came, the old man passed away and behold all things have become new. Our spirits are now perfect and have been given Spiritual deposits to draw from within. (Ephesians 1).
Jesus spent forty days instructing them of this major revelation.