18 Therefore He has mercy on whom He wills, and whom He wills He hardens.
Paul spoke corporately in verses 14 to 18. Israel’s hardening as a nation will not last forever. She will respond to God at the Second Coming (11:11-32). God will remove her hardness then, when He fulfills His unconditional covenants.
and whom He wills
The word “will” indicates God’s resolve or purpose. God resolved to use Pharaoh’s choices in His plan; He used an incorrigible person to advance His purposes. God showed by the plagues of Egypt that man cannot act autonomously, independent from God.
“Hardens” connotes to make hard or to make stubborn. In a number of places Pharaoh hardened his own heart (Ex 4:21; 7:3; 7:13-14, 22; 8:15, 19, 32; 9:7, 34-35). Pharaoh was obstinate. He produced his own negative volition (8:15, 32; 9:34).
It is linguistically possible to translate “hardened” as made strong, strengthen (1 Sa 23:16; 2 Sa 11:25). The idea in the two references is to strengthen and give courage. We can see the idea of “strengthen” in Job 4:
Job 4: 3 Surely you have instructed many, And you have strengthened [hardened] weak hands.
Without context the word “hardened” is morally neutral. It simply means firmness in order to stick to a course. God made Pharaoh firm or stubborn to keep on a course that he had already chosen. It was each successive plague that made him more and more hard toward God. The plague was the precipitating event of his hardness.
God warned Pharaoh that it was He Himself who made Pharaoh’s heart strong toward his object, so he had better think twice about his successive actions. God was responsible for the plagues, but Pharaoh was responsible for his reactions, albeit God let him or helped him to become obdurate. God’s part was the confirmation of Pharaoh’s stubbornness.
Sometimes in Semitic languages the occasion of an event is the origin of the situation rather than the primary cause. The cause remains hidden in this kind of usage; in this case, it is the plagues that hardened Pharaoh, but that remains hidden, making it appear that God is the direct cause. God says in effect, “I know my decisions will cause Pharaoh to go negative in volition toward me.” The plagues, then, were the occasion for Pharaoh’s hardness.
Sunlight shining on the earth hardens clay but, on the other hand, causes things to grow. The effect of what God did in the plagues hardened Pharaoh’s heart. These two verses refer to the effect rather than the cause, and not to a specific act of God:
Ex 7: 3 And I will harden Pharaoh’s heart, and multiply My signs and My wonders in the land of Egypt.
Ex 13: 15 And it came to pass, when Pharaoh was stubborn about letting us go, that the Lord killed all the firstborn in the land of Egypt, both the firstborn of man and the firstborn of beast. Therefore, I sacrifice to the Lord all males that open the womb, but all the firstborn of my sons I redeem.
However, it is also true that God put things in Pharaoh’s life that caused him to harden his heart toward God and His plan for Israel. God was not arbitrary in the way He dealt with Pharaoh. He dealt with him on the basis of his own volition. Pharaoh was accountable for his own actions.
God puts those who persistently harden themselves into a state of hardness.
God never hardens people who do not first harden themselves. Exodus repeatedly affirms that God hardened Pharaoh’s implacable heart (Ex 9:12; 10:1, 20, 27; 11:10; 14:8). In some situations, it was one of the plagues that hardened Pharaoh’s attitude. God shuts in the sinner by his sin. Pharaoh shut himself up by being hardened in sin; He was destined to live as a hardened person to sin (Ex 13:15).
The sinner cannot sin without God’s concurring with it. Concurring does not mean He agrees with it. What God permits is what God does. The sins of those who oppose God are involved in the way God works His plan. God’s opposition serves His purpose. God’s hardening of Pharaoh resulted in God’s displacement of His glory and power. Although God put things in Pharaoh’s way to harden him, that does not make his negative volition is any less his choice.
Ps. 76: 10 Surely the wrath of man shall praise You; With the remainder of wrath You shall gird Yourself.