Impeccability of Jesus Christ

The doctrine of Immutability demands the Impeccability of JesusChrist. The Bible clearly teaches that God was manifest in the flesh~1Timothy3:16. Jesus Christ the same yesterday, and today and forever Hebrews13:8. 1 Timothy 3:16 does not require any interpretation and it is explicit about the humanity of Jesus Christ. Hebrews 13:8 is explicit about the immutability of Jesus Christ. God the Father’s Decree is that the redeemed should be changed to the image (impeccability of Jesus Christ). Our glorious hope is that we all will serve God for ever without a shadow of disobedience. What is sin? Disobedience to God is sin. Another simple way of understanding the impeccability of Jesus Christ is: Ask this question to yourself. Can you disobey yourself? No Never.. you cannot disobey yourself. Even if you broke a resolution it was because you chose to do it. Now ask this question. Can God disobey Himself? No it is not possible for Him to disobey Himself. Since Jesus is God it was and is never possible for Him to disobey Himself. There you go.

John 6 -38:- For I have come down from heaven not to do my will but to do the will of him who sent me.

This means Jesus had his own will, but he choose to do the will of God instead. The situation is same in Romans 7. When we recieve HolySpirit we get to know the will of God, but we keep stuggling between our will (flesh) and God's will (will of Holy Spirit). But Jesus did not have this struggle because he was completely obident to God's will.
Philippians 2-8:-
And being found in appearance as a man,
he humbled himself
by becoming obedient to death—
even death on a cross!
Therefore God exalted him to the highest place
and gave him the name that is above every name

So it was obedience that exalted Jesus not a lack of his will as mentioned by you.