18 Therefore He has mercy on whom He wills, and whom He wills He hardens.
The emphasis here is on God’s the hardening of a nation, not Pharaoh’s hardening of himself. Israel’s hardening is temporary and partial (11:26-31).
Mercy and hardening are antithetical. Both mercy and hardening depend on God’s sovereign will. God judicially abandons people to the hardening influence of sin itself.
The “having mercy” and the “hardening” are not necessarily exclusive in this verse. God can do both or either to each. God can either use Israel or reject her for His purposes, as He sees fit. The direct application of this verse is to Israel as a nation.
Ro 11:7, What then? Israel has not obtained what it seeks; but the elect have obtained it, and the rest were blinded.
Ro 11:25, For I do not desire, brethren, that you should be ignorant of this mystery, lest you should be wise in your own opinion, that blindness in part has happened to Israel until the fullness of the Gentiles has come in.
God will further harden those who are persistently hardened.
The direct hardening in this verse is a reference to Pharaoh’s implacable attitude, his rebellion against God. The Exodus passage asserts both that Pharaoh hardened his own heart and that God hardened his heart. God worked providentially to harden Pharaoh so that he would do His purpose. God hardened Pharaoh’s calloused heart of unbelief by challenging his insolence through further miracles. Pharaoh’s momentum of unbelief made him even more impervious to God’s plan for Israel.
We should not confuse the general hardening of unbelief with God’s providential hardening. God hardened Pharaoh at particular times for a particular purpose for the time in which he lived. God brought him to a state of mind where he would not let Israel leave Egypt, so that His glory would be manifest to the world.
The theodicy in this argument is that God is free to move people and events to accomplish His purpose at any point in time. He can use a Pharaoh for His purposes to bring Israel into the Promised Land. The point is not a salvation issue but an issue of God’s sovereign working to keep His promises to a nation. God can use hardness to carry out His purpose.
There is nothing in this verse about the hardening of a sinner toward salvation. Thus, the theodicy relates to God’s sovereignty in dealing with Israel. God extended mercy toward Israel in the way He dealt with Pharaoh. His saving power toward Israel nationally was to the glory of His name.