What does Genesis 42:18 mean?

Three days have passed since Joseph, now governor of Egypt, has locked all ten of his older half-brothers in prison (Genesis 42:17). The men don't recognize Joseph. Twenty years passed between when they sold him as a slave (Genesis 37:28) and when they came to Egypt to buy grain (Genesis 42:1–5). Though he recognizes them, Joseph keeps his secret and intimidates them into giving more information about the family (Genesis 42:6–16).

Some commentators suggest Joseph was unsure what to do with them. Later passages make it clear he has no mind for revenge (Genesis 42:23–24; 43:30; 45:1–5; 47:11–12). Later, Joseph will even conclude that God meant for him to come to Egypt all along, to save lives (Genesis 50:15–20).

Now, Joseph seems resolved. Given time to process the situation, he has decided on a course of action. He declares this choice is inspired by his fear of God. This may be simply a statement for show—Joseph indeed believes in God, but he might be implying that his actions are being tempered by pagan mercy. Also, his words suggest their lives continue to hang in the balance. His statement that he feared God may have confused them, as well; Egyptians worshiped many gods.