Thomas Merton understood it well:
The Resurrection of Christ is ... the heart of the Christian faith. Without it, the death of Jesus on the Cross is no more than a tragedy of an honest man - the death of a Jewish Socrates. Without the Resurrection, the teaching of Jesus is simply a collection of incoherent fragments with a vague moral reference: the Gospels lose most of their meaning.
The teaching and the miracles of Christ were not meant simply to draw the attention of men to a doctrine and a set of practices. They were meant to focus our attention upon God Himself revealed in the Person of Jesus Christ. Once again, theology is essentially concrete. Far from being a synthesis of abstract truths, our theology is centered in the Person of Jesus Himself, the Word of God, the Way, the Truth, and the Life. ...
Without the Resurrection, there is no sharing in the divine life. The death of Jesus on the Cross expiated our sins, but it was only after He had risen that He breathed upon His disciples, giving them the Holy Ghost with the power to forgive sin, to baptize, to teach and preach to all nations and to renew His life-giving sacrifice.
If Christ is not risen from the death then it is futile to say that He lives in His Church and in the souls of all Christians. For when we say that Christ lives in us, we do not mean that He is present in our minds as a model of perfection or as a noble memory or as a brilliant example: we mean that by His Spirit He Himself becomes the principle of new life and new actions which are truly and literally His life and His actions as well as our own. It is not metaphor for the Christian to say with St. Paul: "I live, now not I, but Christ liveth in me" (Galatians 2:20).
But in the mind of St. Paul the Resurrection of Christ demands our resurrection also, and the two are so inseparable that "if there be no Resurrection of the dead, then Christ is not risen again" (I Corinthians 15:13). It is clear then that the general resurrection is so fundamental a doctrine in the Christian faith that no man who does not accept it can truly call himself a Christian. For St. Paul adds: "If Christ be not risen again, then is our preaching vain and your faith is also vain" (I Corinthians 15:17).
If our whole faith rests on the Resurrection of Jesus, if the Holy Ghost comes to us only from the Risen Christ, and if the whole of God's creation looks to the general resurrection in which it will share in the glory of the sons of God, then for a Christian the "common good" is really centered in the Resurrection of Christ from the dead. Anyone who wants to penetrate into the heart of Christianity and to draw forth from it the rivers of living water that give joy to the City of God (Psalm 45:5) he must enter into this mystery.
No Man Is An Island (1955)