Hebrews 5:8
Though He were a Son, yet learned He obedience by the things which He suffered.
When the Lord Jesus, the Son of God, became a man, He learned what obedience was and what it cost. It cost Him rejection by His own people; an unjust trial in which He was condemned to death; the forsaking of God while He was punished for our sins on the cross. And knowing ahead of time what it would cost Him, He was still willing to be the sin-bearer. He really did learn the cost of obedience.