W.G.T. Shedd on Romans 9:18

Here is Shedd glorifying himself over Him chopping and magnifying himself over the One moving (Isaiah 10:15): 

"Ver. 18. A conclusion of the apostle, introduced by [ara oun], from both of the divine affirmations: that to Moses, and that to Pharaoh, [on] in both instances denotes an actually existing individual, and not an ideal one: a real object upon whom the action designated by [eleei] and [sklerunei] terminates. God never elects or rejects a nonentity. It, also, in both instances, denotes a sinful individual; otherwise, he would not be an object of the merciful action in one case, and of the 'hardening' action in the other. God never forgives and never 'hardens' a holy being. This pronoun is fatal to the supralapsarian theory, which, in the order of decrees, places the decree of election and reprobation, before the decree to create man and to permit the origin of sin by man's self-determination ...
Compare Deut. ii. 30; Ex. iv. 21; xi. 10; Josh. xi. 20; Isa. Ixiii. 17... Not to show mercy to a man is, in St, Paul's use of the word, to  'harden' him. To harden is, not to soften. Hardening is not the efficient action of God, since Pharaoh is said to have hardened his own heart, Ex. viii. 15,32; ix. 34; x. 16. The agency of God in hardening is inaction, rather than action. The Holy Spirit does not strive at all with the human will (Gen. vi. 3), and so permits the already sinful man to confirm himself in sin, by pure and unhindered self-determination. The restraints of conscience, and of the providential circumstances amidst which the man lives, may continue, but are overborne by the sinful will. This is the negative aspect of the hardening.

But besides this, there may be a positive withdrawal of these restraints. This is punitive action, intended as retribution for past resistance of restraining circumstances and influences. See the explanation of [paredoken] in Rom. i. 24. In the instance of Pharaoh, the hardening included both of these features. God left the king of Egypt to his self-will, and also withdrew the restraints that tended to check it. The charge of necessity, in such a reference is absurd. No more unhindered liberty can be conceived of, than this. The human will is left severely alone, to find the reason and source of its impulse wholly within itself. Sin is a more intense and wilful form of self-determination than holiness is; because, unlike the latter, it is the product of the human will in its solitary action, without any internal influence from God.

'If hardness follows upon God's withholding his softening grace, it is not by any efficient and causative act of God, but from the natural hardness of man. When God hardens a man, he only leaves him to his stony heart. God infuseth not any sin into his creatures, but forbears to infuse his grace, and to restrain their lusts, which, upon the withdrawal of restraints, work impetuously. When a man that hath bridled in a high-mettled horse from running, hath given him the reins; or a huntsman takes off the string that held the dog, and lets him run after the hare, are they the efficient cause of the motion of the one, or the other? No, but the mettle and strength of the horse, and the natural inclination of the hound: both of which are left to their own motions, to pursue their own natural instincts' (Charnock, Holiness of God).

'Five times it is said that God hardened Pharaoh's heart; three times that Pharaoh hardened his own heart. Pharaoh, then, was hardened differently by God, from what he was by himself. He hardened his own heart by wilfully resisting Moses, and despising God, and the judgments of God. God hardened his heart, by not converting his already hard heart into a heart of flesh.' Pareus, in loco. 'The perdition of sinners,' says Calvin (Instit. 111. xxiii. 8), 'depends upon the divine predestination in such a manner that the cause and matter of it are found in themselves'" (W.G.T. Shedd, A Commentary on the Epistle to the Romans, pp. 291-293; underlining mine--CD)