Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new. – 2 Corinthians 5:17

The text saith that we are new creatures through being in Christ. How comes that about? We have known persons inveigh very earnestly against the doctrine that men are saved by a simple faith in Jesus Christ. That is the gospel, and nothing else is the gospel, and those who do not preach that truth know nothing of God’s gospel at all; for it is the very soul and essence of the gospel -the article, as Luther used to say, by which a church stands or falls. We are saved by a simple faith in Jesus, but these people argue against this on the ground that there must be a great moral change in man before he can be reconciled to God and made meet to be with God for ever. But, my brethren, if the text be true, that those who are in Christ are new creatures, what greater change than this can be desired? I know no language, I believe there is none, that can express a greater or more thorough and more radical renewal, than that which is expressed in the term, “a new creature.” It is as though the former creature were annihilated and put away, and a something altogether new were formed from the breath of the eternal God, even as in the day when the world sprang out of nothing, and the morning stars sang together over a new-made universe. Such is the fruit of being in Christ, to be a new creature. And what, ye moralists, want ye more than this? What, ye pretenders to perfection, what, ye mystic spiritualists, who strive after a strange holiness to which ye never attain, what, ye that bind heavy burdens upon men’s shoulders which ye do not touch with your fingers yourselves, what want ye more than this, for a man to be absolutely made a new creature by being in Christ? ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0881.cfm