For as in Adam all die, even so in Christ shall all be made alive. 1 Corinthians 15:22

I never heard of any persons being in any other man but Christ; we may follow certain leaders, political or religious, but we are never said to be included in them. We may take for ourselves eminent examples and high models of humanity, but no man is said in that respect to be in another. But this is a grand old scriptural phrase in which the disciple and the follower of Christ becomes something more than an imitator of his Lord, and is said to be in his Master. We must interpret this scriptural phrase by scriptural symbols. We were all of us in the first Adam. Adam stood for us. Had Adam kept the command, we had all of us been blessed. He took of the forbidden fruit and fell, and all of us fell in him. Original sin falleth upon us because of the transgression of our covenant head and representative, Adam the first; but all believers are in the same sense in Christ, Adam the second, the only other representative Man before God, the heavenly Man, the Lord from heaven. Now, as in Adam we all fell, so all who are in Christ are in Christ perfectly restored. The obedience of Christ is the obedience of all His people; the atonement of Christ is a propitiation for all His people’s sins. In Christ we lived on earth, in Christ we died, in Christ we rose, and He “hath raised us up together, and made us sit together in heavenly places” in Himself. As the apostle tells us that Levi was in the loins of Abraham when Melchisedec met him, so were we in the loins of Christ from before the foundation of the world; faith apprehends that blessed truth, and thus by faith we are experimentally in Christ Jesus.~ C.H. Spurgeon

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