Römer 9:18

Therefore hath he--"So then he hath." The result then is that He hath mercy on whom he will have mercy, and whom he will he hardeneth--by judicially abandoning them to the hardening influence of sin itself (Psa 81:11-12; Rom 1:24, Rom 1:26, Rom 1:28; Heb 3:8, Heb 3:13), and of the surrounding incentives to it (Mat 24:12; Co1 15:38; Th2 2:17). Second objection to the doctrine of Divine Sovereignty:

We have here the apostle's solemn profession of a great concern for the nation and people of the Jews - that he was heartily troubled that so many of them were enemies to the gospel, and out of the way of salvation. For this he had great heaviness and continual sorrow. Such a profession as this was requisite to take off the odium which otherwise he might have contracted by asserting and proving their rejection. It is wisdom as much as may be to mollify those truths which sound harshly and seem unpleasant: dip the nail in oil, it will drive the better. The Jews had a particular pique at Paul above any of the apostles, as appears by the history of the Acts, and therefore were the more apt to take things amiss of him, to prevent which he introduces his discourse with this tender and affectionate profession, that they might not think he triumphed or insulted over the rejected Jews or was pleased with the calamities that were coming upon them. Thus Jeremiah appeals to God concerning the Jews of his day, whose ruin was hastening on (Jer 17:16), Neither have I desired the woeful day, thou knowest. Nay, Paul was so far from desiring it that he most pathetically deprecates it. And lest this should be thought only a copy of his countenance, to flatter and please them, I. He asserts it with a solemn protestation (Rom 9:1): I say the truth in Christ, "I speak it as a Christian, one of God's people, children that will not lie, as one that knows not how to give flattering title." Or, "I appeal to Christ, who searches the heart, concerning it." He appeals likewise to his own conscience, which was instead of a thousand witnesses. That which he was going to assert was not only a great and weighty thing (such solemn protestations are not to be thrown away upon trifles), but it was likewi…

9:18 he chooses to harden the hearts of others so they refuse to listen: Pharaoh refused to let Israel go because his heart was hardened. God hardened Pharaoh’s heart (Exod 9:12), and Pharaoh hardened his own heart (Exod 8:15).