Jesus, the Word, could not be made at all, that is, created, since he is the Maker and Creator of all things. Therefore, he himself could not be made or created - nor was he, nor could he be, made, converted, and changed into flesh. The divine nature in Christ could not be changed into human nature, for he is the Lord that changes not. He is the same in the "yesterday" of eternity, in this day of time, and "forever" to all eternity.
By the incarnation nothing is added to, nor altered in, the divine nature and personality of Christ. The human nature adds nothing to either of them; they remain the same as they ever were. Christ was as much a divine Person before his incarnation as he is since. But, as other scriptures explain it, God the Word, or Son, was made and became "manifest in the flesh"; the Son that was in the bosom of the Father, the Word of life that was with him from all eternity, was manifested in the flesh in time to the sons of men to to take away sin and destroy the works of the devil (1 Tim. 3:16; 1 John 1:1-2; 3:5,8). And the incarnation of the Word or Son of God is expressed and explained by his taking on flesh and blood; and by taking on himself the nature of man.
Both natures, divine and human, are united in one Person, and there is but one Lord and one Mediator between God and man. The Nestorians so divided and separated these natures, as to make them distinct and separate Persons, which they are not. And the Eutychians, running to the other extreme, mixed and confounded the natures together, interpreting the phrase "the Word was made flesh" as the divine nature being changed into the human nature and the human nature into the divine nature. But this is to make Christ neither truly God, nor truly man; the one nature being confounded with and swallowed up in the other. But this union of natures is such, that though they are closely united and not divided, yet they retain their distinct properties and operations.
Adapted from A Body of Doctrinal Divinity, Book 5, Chapter 1, by John Gill.