Jamieson, Fausset and Brown on Luke 2:6

6. while they were there, the days were accomplished that she should be delivered--Mary had up to this time been living at the wrong place for Messiah's birth. A little longer stay at Nazareth, and the prophecy would have failed. But lo! with no intention certainly on her part, much less of Cæsar Augustus, to fulfil the prophecy, she is brought from Nazareth to Bethlehem, and at that nick of time her period arrives, and her Babe is born (Psa 118:23). "Every creature walks blindfold; only He that dwells in light knows whether they go" [Bishop Hall].