The initial dialogue between Moses//Aaron and Pharaoh plays off the theme of identity. "Who is YHWH?" asks Pharaoh--as Moses asked "who am I?" and looking ahead the story will climax (14:4, 18) with the divine declaration that "the Egyptians will know I am YHWH God." (this latter expression will reappear 1 Samuel 17:46). Thematically, this is the major theme of the narrative- the discovery of the true God vs the gods of the pagans.
5:1 shalach (send, set free, send away; to stretch forth) this verb occurs frequently. In Exodus 2 the daughter of Pharaoh sent her maid to get baby Moses. In 3:10-20 it occurs in six verses, each time repeating that God will send Moses, culminating in the petition in v20 "I will stretch forth" My hand...Pharaoh will "send forth" My people. It will be used five times in chapter four, twice here and a third time in chapter five. Pharaoh refuses, which begins the long process of the hardening of his heart. He is an oppressor and will be enamored with his own power. He is not open to God speaking to him (he knows not the Lord). So the second request (v3) to go a three day journey to sacrifice to God goes unheeded. The threat of "pestilence or sword" is echoed in v 21-22 (when Israel confronts Moses and Aaron), but it is what will befall Egypt. William Propp points out that Moses did not follow the orders of God directly--the elders are absent, he did not do the signs or make the threat on the first born son. (as is often the case in SS, the narrator does not give a comment so as to provide us God's reaction to this) We also note that the address to Pharaoh is expressed in prophetic style ("thus says the Lord") and that the interaction lacks any of the expected respectful groveling due an Ancient Near East monarch.
5:5 the response of Pharaoh is the opposite of what Moses seeks. Pharaoh (as a true despot) blames the oppressed for being lazy. Many contemporary commentators draw parallels to the social injustices in every society and the way power speaks to the under class. The Lord has come to rescue the poor and needy. Hebrew foremen serve as collaborators with the Egyptians and the work load is increased (they must gather their own straw now to make the bricks). The increased oppression, which is an attempt to exert greater control, fails. Making things worse creates a greater longing for freedom. The language thematically connects to Genesis and the people spread out through the land, just as animals and humans on the earth do in creation. (also v. 8 'idlers' comes from the verb "to let go, to relax, found in the 'bridegroom of blood episode) God blesses in accord with His original intent and the Pharaoh stands against God's blessing.
The dire situation spirals into worse and worse, as expressed in the dialogue of the various parties. The harder task, the more demanding situation and the beating of the overseers add to the tension culminating in v21 where the people of Israel accuse Moses and Aaron, even asking God to judge them (!) for the hardships imposed by Pharaoh. Moses, in turns, complains to God. "Why have you done this harm to your people, why did you send me?" The irony is God's salvation makes things worse, to begin with. In Mark 6 Jesus said "pick up your cross and follow me." The reality of a fallen world is often times difficult struggles and pain, even if God is saving you. The travails of Israel will continue. God appears slow to save His people. The chapter ends shrouded in worry and doubt. Will God keep His word to His people? Chapter Six will begin with a wonderful declaration of God's intent!