In Romans 9:19, we read "Thou wilt say then unto me, Why doth he yet find fault? For who hath resisted his will?" This concept that none can resist God's will is strongly supportive of Calvinism. Calvinism, of course, has the concept of Irresistible Grace (those whom God wills to save will be saved), which also ties in quite well with Total Depravity (mankind is incapable of choosing God), and even Limited Atonement (the cross covers only the elect).
There is, however, one problem; sin. Sin, by definition, is the opposition to God's will. To say none can resist God's will is to either say none can sin, or to say God wills for people to resist His will, (that is, to do what we are claiming they cannot do). But this brings up another problem, because the Bible really does say "who hath resisted his will"? Using philosophy against the Bible never goes well. What the Bible says is true, straight from the mouth of God, and so if we find some issue with it, we are the ones at fault. Calvinists should take note of this, for they often use philosophy against Scripture.
But is this what I did above? To an extent, you could argue yes. However, I can actually prove this philosophy with other Scriptures. Scripture constantly, almost like a beating drum, affirms that man resists God's will. We have explicit statements, like when Luke 7:30 tells us the Pharisees and lawyers rejected God's will for them by not being baptised by John. But we also have strong implications that men have done what God never intended them to do. One example can be seen in Jeremiah 7:31: "And they have built the high places of Tophet, which is in the valley of the son of Hinnom, to burn their sons and their daughters in the fire; which I commanded them not, neither came it into my heart."
Note God's words here. "...neither came it into my heart". Does this sound like a God who wills His people to build high places of Tophet or burn their sons and daughters? No, it sounds like He didn't ask them to do this, nor did He plan for it. They did it on their own, and like all sin, this ticked God off.
But this raises the question, if people can resist His will, how do we deal with Romans 9:19 seemingly disagreeing with the possibility? Simple. We take the verse in context. What is the context of Romans 9:19?
"I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost, That I have great heaviness and continual sorrow in my heart. For I could wish that myself were accursed from Christ for my brethren, my kinsmen according to the flesh: Who are Israelites; to whom pertaineth the adoption, and the glory, and the covenants, and the giving of the law, and the service of God, and the promises; Whose are the fathers, and of whom as concerning the flesh Christ came, who is over all, God blessed for ever. Amen. Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel: Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed. For this is the word of promise, At this time will I come, and Sarah shall have a son. And not only this; but when Rebecca also had conceived by one, even by our father Isaac; (For the children being not yet born, neither having done any good or evil, that the purpose of God according to election might stand, not of works, but of him that calleth;) It was said unto her, The elder shall serve the younger. As it is written, Jacob have I loved, but Esau have I hated. What shall we say then? Is there unrighteousness with God? God forbid. For he saith to Moses, I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion. So then it is not of him that willeth, nor of him that runneth, but of God that sheweth mercy. For the scripture saith unto Pharaoh, Even for this same purpose have I raised thee up, that I might shew my power in thee, and that my name might be declared throughout all the earth. Therefore hath he mercy on whom he will have mercy, and whom he will he hardeneth."
There is a lot to unpack. Here, Paul goes through a lot of Old Testament references, all of which are necessary to fully understand Romans 9. If you have only Romans 9, but don't know the Old Testament Scriptures it cites, you may well become a Calvinist. But looking through these Old Testament Scriptures, we actually don't get a Calvinist impression. Rather, we see, as God continues to say, that God "...endured with much longsuffering the vessels of wrath fitted to destruction:" (Romans 9:22).
Notice how even in Romans 9, God describes Himself as merely enduring with the wicked (who, by the way, He takes no pleasure in the death of). It's not something He wills, it's something He tolerates in order to get His will. But the wicked are actually freely complicit in this. For example, the passage mentions Pharaoh, and how he was raised up that God might show His power through Him, and that His name might be declared throughout the Earth. But what we see from the get go in the Old Testament is that even without God's intervention, Pharaoh would not have let the people go unless He was compelled with a heavy hand (Exodus 3:19-20). In Exodus 8:15, we see that Pharaoh hardens his own heart, simply because the Lord gave respite to Egypt.
We see in context, therefore, that Romans 9:19 does not mean no one can resist God's will in any way what so ever. In fact, it does not seem to apply to individual salvation at all. Instead, it seems to show that God cannot be impeded in His earthly purposes. If God wants to build and prosper a nation, He can build and prosper a nation. If God wants to destroy a nation, He can destroy a nation. All of this, He does for sake of His glory. That includes taking what we mean for evil and using it for good. To do this, He doesn't need to cause us to sin, for we do that pretty well on our own. But Scripture is clear on this: God "...will have all men to be saved, and to come unto the knowledge of the truth."
Therefore, those who refuse God's gift of salvation are resisting His will, being like clay marred in the potter's hands. They have not resisted His will in that they have somehow overpowered Him, just as Christ was not overpowered by the Romans, but they have rejected a gift He so freely offered by Him. Ultimately, it is necessary that free will exists in order for God to truly say that any historical sin "never entered His heart", for if He willed it, it did by definition. But God, of course, is a logical God. If it was impossible to resist God's will full stop, it would be impossible to sin, but it is only impossible to resist His ultimate will.