He learned obedience by the things that He suffered. Hebrews 5:8 KJV
He learned obedience from the things which He suffered. Hebrews 5:8 NASB
He … became obedient unto death, even the death of the cross. Philippians 2:8 KJV
He … becoming obedient to the point of death, even death on a cross. Philippians 2:8 NASB
… by the obedience of One shall many be made righteous. Romans 5:19 KJV
…through the obedience of the One the many will be made righteous. Romans 5:19 NASB
In Eden’s Garden, sin in the form of disobedience invaded our planet and our persons. Adam had one restriction, one “law” to which to bow. He willingly chose to disobey God. From that initial act of rebellion against the will of God, down to the present day, humanity has been marked by asserting our independence of God – “we have turned every one to his own way.” Individually we have strayed in our self-will. The nation of Israel, brought near and privileged, was characterized as a “disobedient and gainsaying nation” (Rom 10:21).
Obedience to God is an indication of loyalty – a loyalty inspired by love and absolute trust in His wisdom and goodness. Obedience thus is not merely compliance with His commands but involves love, trust, loyalty, confidence, and faith. When the last Adam touched down on planet earth, He was marked, in contrast to Adam, by perfect obedience.
Philippians tells us that the entire course of His life was one of moment-by-moment obedience. As is often pointed out, He never became obedient to death as though death had a claim upon Him. His obedience was throughout His life – all the way to the point of death; and further, that death envisioned was a cross death. No desire of His Master was too great for this Servant. The day-to-day steps of obedience would terminate in one final momentous act of obedience involving a cross death. 
The Hebrew writer turns from the tenor of the life of the Lord Jesus Christ to the terminus of His life. Now it is the cost of obedience that is in view. He never learned to obey; but He did learn how costly it was to obey. Though there was cost entailed and experienced throughout His life for His obedience to His Father’s will – hunger during the temptation, misunderstanding, false accusations, reproach – yet the cross was the ultimate display of His obedience, the ultimate cost “learned” in His pathway.
The logic in Paul’s masterful handling of the subject of Federal Headship in Romans 5 contrasts the disobedience of the first Adam with the obedience of the last Adam. Translations vary between the one obedience of One Man and the one obedient act. But the end result is the same: One Man, the last Adam, by His act of obedience, submitting to the Father’s will and accepting the cross, has made it possible for all those who are in Him to be constituted righteous.
In Deuteronomy 21:18-23 a disobedient and stubborn son was to be stoned to death and then hanged on a tree. Yet in God’s wondrous plan of grace to us, the only Obedient Son was crushed beneath the divine justice of God while impaled to a tree.
Consider:
What other contrasts can you draw between Adam and Christ?