Jamieson, Fausset and Brown on Exodus 5:3

3. The God of the Hebrews hath met with us--Instead of being provoked into reproaches or threats, they mildly assured him that it was not a proposal originating among themselves, but a duty enjoined on them by their God. They had for a long series of years been debarred from the privilege of religious worship, and as there was reason to fear that a continued neglect of divine ordinances would draw down upon them the judgments of offended heaven, they begged permission to go three days' journey into the desert--a place of seclusion--where their sacrificial observances would neither suffer interruption nor give umbrage to the Egyptians. In saying this, they concealed their ultimate design of abandoning the kingdom, and by making this partial request at first, they probably wished to try the king's temper before they disclosed their intentions any farther. But they said only what God had put in their mouths (Ex 3:12, 18), and this "legalizes the specific act, while it gives no sanction to the general habit of dissimulation" [Chalmers].