Paraphrase of OP's Inquiry: How does Jesus grow in favor with God if he was already without sin to begin with?
Well, one overlooked aspect of the life of Jesus is that, while he was always sinless, he nevertheless had to learn obedience to be perfected as a source of eternal salvation to those who obey him.
Hebrews 5:8-10 8 Although he was a son, he learned obedience through what he suffered. 9 And being made perfect, he became the source of eternal salvation to all who obey him
So, however perfect Jesus was before, he was imperfect or incomplete as the source of eternal salvation for all who obey until he had learned the requisite obedience. There are basically two types of learning: 1) a kind of book learning where you gain knowledge from simply consuming information or by thinking through a problem, and 2) experiential learning gained by actually doing the thing you intend to learn. Apparently, the type of learning that Jesus needed to become perfect for salvation could only be gained through his experience as a human.
17 Therefore he had to be made like his brothers in every respect, so that he might become a merciful and faithful high priest in the service of God, to make propitiation for the sins of the people. 18 For because he himself has suffered when tempted, he is able to help those who are being tempted. -Hebrews 2:17-18
8 And being found in human form, he humbled himself by becoming obedient to the point of death, even death on a cross. 9 Therefore God has highly exalted him and bestowed on him the name that is above every name, Philippians 2:8-9
The "therefore" of verse 9 above relates the reason for why God so highly exalted Jesus specifically to the obedience that Jesus committed himself to from the point he found himself in human form to the point of his death on the cross. From the moment Jesus found himself in human form till the moment of his death, he had continually increased in favor with God, by progressively doing God's will in total obedience, until he was ultimately perfected as the source of salvation for all who obey him.
So the efficiency of a blemished sinful person's obedience to Christ for the purpose of their own salvation depends ultimately on the progressive obedience of Christ to the Father demonstrated during his earthly life that resulted in him becoming the source of eternal salvation for all those who obey him.
So while it may still seem odd to some that the amount of favor Christ had with God depended upon Christ's obedience to the Father, it should be noted and meditated upon that Christ himself revealed during his time on Earth, that his own relationship with God, the Father, itself depended upon his obedience to the will of the Father who sent him.
John 4:34 “My food is to do the will of him who sent me and to accomplish his work.
John 8:29 And he who sent me is with me. He has not left me alone, for I always do the things that are pleasing to him.”
John 15:10 If you keep my commandments, you will abide in my love, just as I have kept my Father's commandments and abide in his love.