Hebrews 1:3 tells us that the Son “upholds all things by the word of His power.” If the Son never ceased to be God, Hebrews 1:3 must remain true even at the time of His incarnation. So while Mary was holding her son, He was holding her–and the universe–together.
Athanasius (4th c.) articulated the paradox this way:
The Word was not hedged in by His body, nor did His presence in the body prevent His being present elsewhere as well. When He moved His body He did not cease also to direct the universe by His Mind and might. No. The marvelous truth is that being the Word, so far from being Himself contained by anything, He actually contained all things Himself.
. . . At one and the same time—this is the wonder—as Man He was living a human life, and as Word He was sustaining the life of the universe, and as Son He was in constant union with the Father. Not even His birth from a virgin, therefore, changed Him in any way, nor was He defiled by being in the body.
–Athanasius, On the Incarnation
Come and stand amazed, indeed.