Boy Jesus at the temple in Luke 2:
49“Why were you searching for me?” he asked. “Didn’t you know I had to be in my Father’s house?” 50But they did not understand what he was saying to them.
51Then he went down to Nazareth with them and was obedient to them. But his mother treasured all these things in her heart. 52And Jesus grew in wisdom and stature, and in favor with God and man.
Jesus was obedient to his heavenly and earthly fathers all along.
In English, we have this common sense of learning:
My attitude was like this before but I learned the lesson. Now I'm different.
The sense of learning in Hebrews 5:8 is different.
Son though he was, he learned obedience from what he suffered
The stress is on the suffering experience, not on the attitude of obedience.
Thayer's Greek Lexicon
STRONGS NT 3129: μανθάνω
μανθάνω; 2 aorist ἔμαθον; perfect participle μεμαθηκώς; the Sept. for לָמַד; (from Homer down); to learn, be apprised;
The acquisition of knowledge is important through the experience of the learning process.
a. universally: absolutely, to increase one's knowledge, 1 Timothy 2:11; 2 Timothy 3:7; to be increased in knowledge, 1 Corinthians 14:31; τί, Romans 16:17; 1 Corinthians 14:35; Philippians 4:9; 2 Timothy 3:14; Revelation 14:3;
b. equivalent to to hear, be informed
In terms of attitude, Jesus was perfectly obedient to start with. He acquired more and more knowledge about incidences of obedience through time in the learning/training episodes/process.
c. to learn by use and practice; (in the preterite) to be in the habit of, accustomed to: followed by an infinitive, 1 Timothy 5:; Titus 3:14; Philippians 4:11 (Aeschylus Prom. 1068; Xenophon, an. 3, 2, 25); ἔμαθεν ἀφ' ὧν ἔπαθε τήν ὑπακοήν, Hebrews 5:8
The word is related to practical training. Interestingly, in AI Machine Learning, the same training sense is used. The machine learner learns from episodes of experience through training epochs.
Wasn't the Lord, Jesus, fully obedient to the Father?
Was suffering necessary to learn obedience?
It was necessary as a matter of training obedience. It was the training procedure.
Suffering and Crucifixion of the Lord was atonement for humanity.
Right. Dying on the cross was part of his obedient suffering experience.