I have heard, during my entire Christian life, that "Jesus was both fully God and fully man". What is the biblical basis for this claim, in particular the "fully man" part of this doctrine?
The biblical basis for Jesus Christ being spoken of as both fully God and fully man is found in the following biblical texts, of which this is just a small sample. If you want the full biblical basis, you would best read a book, or a chapter in a book where all the Bible verses are systematically dealt with. I have grouped related verses together, which deal with particular aspects of assorted evidences.
His Pre-existence: John 1:1-3; 8:56-58; 17:5 & 24; Phil. 2:6; Col. 1:17; Heb. 1:2; Rev. 1:8
His Deity: Psalm 110:1 with Mark 12:35-37; Isaiah 7:14 with Matthew 1:23; Isaiah 9:6; Malachi 3:1; John 20:28; Romans 9:5; Phil. 2:6; Col. 1:19; 2:9; Titus 2:13; Heb. 1:3, 6, 8; James 2:1; 2 Peter 1:1
His Humanity: Matthew 1:1-17 & 23; and a great number of times where he calls himself the son of man, e.g. 8:20 & 12:40 & 26:64; Luke 1:29-33; John 1:14 & 29-30; 3:14; Acts 7:56; 1 Cor. 15:47; 1 Tim.2:5; Rev. 1:13 & 14:14
That incomplete list should get you started.
2Very Good Answer. I like that you added his Pre existence Dec 29, 2022 at 11:58
In addition to the excellent catalogue produced by @Anne , I would add one striking example of the union of Deity and humanity in the Person of Jesus Christ which is expressed in scripture, being the remarkable vision of one "like the son of man", Revelation 1:13, of whom it is conveyed - firstly :
... and he had in his right hand seven stars: [Revelation 1:16 KJV]
and, secondly :
... he laid his right hand upon me, saying unto me, Fear not. [Revelation 1:17 KJV]
The hand that holds seven stars within it cannot possibly be a human hand. It must be the same (Divine) hand of him who said :
... my right hand hath spanned the heavens. [Isaiah 48:13 KJV]
Yet, the right hand laid upon John, with the comforting words, 'Fear not', is - most definitely - a matter of humanity. And more than that, it is a matter of kindness, of comfort and of reassurance in the face of awesome revelation.
And that right hand is scarred, which was previously offered ('reach forth thy finger', John 20:27) to a doubter in proof that he is risen from the dead, for it was pierced, in crucifixion ; a ransom for many, Mark 10:45 and Matthew 20:28.
For Jesus Christ is he by whom all things were made, a co-Creator of all that exists, for 'all things were made by him and without him was not anything made that was made', John 1:3 ; yet he is also the one mediator between Deity and humanity : 'humanity Christ Jesus' (as the literal Greek conveys the words in 1 Timothy 2:5).
... ανθρωπος χριστος ιησους, anthropos christos jesous [TR]
Thus he is the one for whom Job longed . . . a 'daysman to lay his hand upon us both' Job 9:33. Who can lay one hand upon omnipotence, a hand that easily encompasses the stars, and he can lay the other upon such as John, saying 'Fear not' though he be of such divine power and ability . . . .
. . . and he can do such, now, in this our day, for he is risen from the dead and dieth no more.