What does Exodus 5:16 mean?

The "straw" mentioned here is the typical kind: unused stalks from harvested plants. Egypt enslaved Israel (Exodus 1:13–14) and forced them to make bricks. These were made of mud and sand mixed with straw. Egyptian slavery was already brutal (Exodus 1:11). But when Moses demanded release of the people (Exodus 5:1–5), Egypt's ruler, Pharaoh, was annoyed. In retaliation, he stopped providing the slaves with straw, forcing them to find their own (Exodus 5:6–9).

Here, the Hebrew slaves assigned as supervisors complain that they are being beaten for no good reason (Exodus 5:14–15). They continually refer to themselves as Pharaoh's servants—showing submission and humility—while pointing blame at the Egyptians who won't provide raw materials.

For the seventh time in this passage the word "straw" is again noted. "No straw" is given. The foremen refer to themselves as Pharaoh's servants as in verse 15. However, they repeat Pharaoh's command to "make bricks" as an impossible requirement. They call themselves "servants" a third time and then refer to being beaten. They claim the ones at fault who deserve punishment are the Egyptians.

Pharaoh will respond with a dismissive reference to Moses' request for freedom to worship (Exodus 5:17). The king's intent is to send a message: if you have time to think about freedom, you aren't being worked hard enough. This is meant to intimidate the Hebrews. It's also intended to generate resentment against Moses and Aaron—which it does (Exodus 5:20–21).