Yes, I wonder how Jonathan Edwards, for example, in all of his expressed non-Jesus-like hatred toward humanity, could be convinced that he was, in fact, among the elect, assuming that Calvinism is indeed true.
But how could Calvinism be true? How could all of these Calvinists have missed the clear argument for Universalism in these simple words?
Premise 1: God desires all be saved. (e.g., 1 Timothy 2:4: “[God] who desires (thelo) all people to be saved and to come to the knowledge of the truth.”)
Premise 2: God accomplishes whatever He desires. (e.g., Isaiah 55:11: “So will My word be which goes forth from My mouth; It will not return to Me empty, Without accomplishing what I desire (thelo, from the Septuagint), And without succeeding in the matter for which I sent it.”)
Conclusion: All will be saved.
The key word in this syllogism is the Greek verb thelo. When it is used in the Bible with respect to God, it always denotes something that will indeed happen. So, if God desires (thelo) it to happen, it will happen, without exception. (There is an apparent exception in Romans 9:22 in a few Bible versions, but that exception appears not to be a genuine exception, for the word that would make the verse an exception is “although,” and that word is not present in the original Greek of this verse, and the vast majority of translations do not include it.)