William Burkitt on Luke 2:39

Here we see the truth and reality of Christ's human nature: he grew as we do, from infancy to childhood, from childhood to youth and manhood. To his divine nature no accession or addition could be made, for that which is infinite cannot increase. The Deity was infinite in Christ, so was not the humanity, but capable of additions: and accordingly as Christ grew up in the stature of his body, the faculties of his mind increased, through the grace and power of God's Spirit upon him.