71 Then, as for Faustus' objection to the spoiling of the Egyptians, he knows not what he says. In this Moses not only did not sin, but it would have been sin not to do it. It was by the command of God, who, from His knowledge both of the actions and of the hearts of men, can decide on what every one should be made to suffer, and through whose agency. The people at that time were still carnal, and engrossed with earthly affections; while the Egyptians were in open rebellion against God, for they used the gold, God's creature, in the service of idols, to the dishonor of the Creator, and they had grievously oppressed strangers by making them work without pay.
Thus the Egyptians deserved the punishment, and the Israelites were suitably employed in inflicting it. Perhaps, indeed, it was not so much a command as a permission to the Hebrews to act in the matter according to their own inclinations; and God, in sending the message by Moses, only wished that they should thus be informed of His permission. There may also have been mysterious reasons for what God said to the people on this matter. At any rate, God's commands are to be submissively received, not to be argued against.
The apostle says, "Who has known the mind of the Lord? Or who has been His counsellor?" Whether, then, the reason was what I have said, or whether in the secret appointment of God, there was some unknown reason for His telling the people by Moses to borrow things from the Egyptians, and to take them away with them, this remains certain, that this was said for some good reason, and that Moses could not lawfully have done otherwise than God told him, leaving to God the reason of the command, while the servant's duty is to obey.
Source: Reply to Faustus the Manichaean (New Advent)