This is one of my favorite quotes from Calvin's universalist statements. This is from John Calvin's Commentary on Romans 5:18 (the link goes to one of my previous blog posts where one can read the quote in a larger context and get more of my thoughts on the subject):
He makes this favor common to all, because it is propounded to all, and not because it is in reality extended to all; for though Christ suffered for the sins of the whole world, and is offered through God’s benignity indiscriminately to all, yet all do not receive him.
Justification is "propounded" (i.e., offered or set forth) to all, but not in reality "extended" to all. That is, all men are offered justification, but not all men are actually justified. That's Calvin's meaning here.
Calvin explains that this is so "for though Christ suffered for the sins of the whole world...." No question about the meaning of that, is there? It's not out of context, and it isn't denied by anything in the quote itself. Calvin is asserting this: "Christ suffered for the sins of the whole world...."
Notice the parallelism between Christ's suffering for all on the one hand and the indiscriminate offer to all on the other hand. The "all" here must be really "all," because the suffering is for "the whole world" and the offer is "indiscriminately to all." The ideas explain and reinforce one another. And it isn't "the world of the elect," because some of those for whom Christ died and to whom he is offered, "do not receive him."
It couldn't be clearer.