The question, which I am answering (as it stands at 19:09 GMT on 03 February 2020) is :
How can Paul say his apostleship is not from men, neither through man ?
Paul makes clear in Galatians 1:1 that his apostleship was not through man, or by man. It was through Jesus Christ and through God Father (literal). If not through man or by man and if through (that is to say by the agency of an intermediary) Jesus Christ and God Father, then who was the originator of this apostleship ?
I would say it is the same person as Paul refers to in connection with eldership :
Take heed therefore unto yourselves, and to all the flock, over the which the Holy Ghost hath made you overseers, to feed the church of God, which he hath purchased with his own blood. [Acts 20:28 KJV]
The Holy Spirit made certain men overseers at Ephesus. The 'blood of his own' (literal) is that with which God (the Holy Spirit) purchased the gathered company at Ephesus. And it was God, the Holy Spirit, who appointed individuals to oversee that gathered company.
Likewise, Paul's apostleship as to the intermediary agency (through) is Jesus Christ and God Father. But if through those two persons, then who was the instigator ?
None other than the same Holy Spirit who made overseers at Ephesus.
And we see that all the company of the redeemed are so appointed :
Forasmuch as ye are manifestly declared to be the epistle of Christ ministered by us, written not with ink, but with the Spirit of the living God; not in tables of stone, but in fleshy tables of the heart. [2 Corinthians 3:3 KJV]
By the personal operations of the Holy Spirit, under the intermediary agency of the ministry of the apostle, the Spirit of the Living God wrote upon the hearts of those who received that word and they became living epistles, known and read of all men.
Thus none of this is of man or by man.
It is not human in origin. It is of Spirit.
Whether the birth of God's children . . . .
Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God. [John 1:13 KJV.
Or the making of overseers . . .
Or the calling and sending of an apostle . . . .
. . . all is of God, who is Spirit (John 4:24).
It was the Holy Spirit who, after the conversion of Saul of Tarsus and after some time during which he had fellowship with other Christians, marked out Barnabas and Saul :
As they ministered to the Lord, and fasted, the Holy Ghost said, Separate me Barnabas and Saul for the work whereunto I have called them. [acts 13:2 KJV]
This is not of man, but of God.
Nor was the conversion of Saul anything to do with men, for it was a voice from heaven and a light above the brightness of the sun which came upon him on the road to Damascus.
Jesus Christ spoke to Saul, but Jesus Christ did not appear, bodily.
Risen from the dead, Jesus said :
Behold my hands and my feet, that it is I myself: handle me, and see; for a spirit hath not flesh and bones, as ye see me have. [Luke 24:39 KJV]
And they gave him a piece of a broiled fish, and of an honeycomb. And he took it, and did eat before them. [Luke 24: 42, 43 KJV]
Jesus rose bodily, they handled him, he ate food in front of them.
And he ascended into heaven.
And from there, from the throne of God, as God, he appointed Paul to be an apostle by the direction of God, the Holy Spirit.