How do we know Christ had to be both God and man?

The necessity for Christ to be both God and man stems from the dual requirements of atonement. Being God means He can fulfill divine justice and satisfy the requirements of perfect holiness as stated in 2 Corinthians 5:19, where it says 'God was in Christ reconciling the world to Himself.' Simultaneously, He must be man to suffer and atone for humanity's sins, as a man brought sin into the world. Without this dual nature, He could not effectively be the mediator needed for redemption. John 1:14 underscores this mystery, stating, 'The Word became flesh and dwelt among us,' illustrating how God took on human form to facilitate salvation.