A central part of the Christian doctrine of the incarnation is that the Son of God ‘becomes’ incarnate. Furthermore, according to classical theism, God is timeless: He exists ‘outside’ of time, and His life has no temporal stages. A consequence of this ‘atemporalist’ view is that a timeless being cannot undergo intrinsic change—for this requires the being to be one way at one time, and a different way at a later time. How, then, can we understand the central Christian claim (...) that the Son of God ‘becomes’ human? This paper examines one such explanation, drawn from a brief remark by Brian Leftow: the Word takes on flesh by exhibiting modal variation with regards to the incarnation. On this account, a timeless God ‘becomes’ incarnate simply due to variation across logical space: at some possible worlds He is incarnate and at others He is not. Modal variation need not, therefore, require temporality: it only requires variation across possible worlds. I draw out the problems with Leftow’s modal claim under the heads of Ersatzism and Genuine Modal Realism about possible worlds, respectively. I argue that in both instances, Leftow’s desired cross–worldly variation of the Son’s incarnation cannot be achieved. (shrink)