When Jesus established the Lord’s Supper, Judas was there. And because Satan had entered into Judas, Satan was also there. The sacrament here is not a reward for the already arrived. Not only so, but it is also used in driving away those who will never arrive. We don’t need to drive anyone away. We don’t need to defend the Table; fencing the Table (as we do) is a matter of guarding ourselves.
In Exodus, when the Lord invited Moses, and seventy elders, to come up on the mountain, and eat and drink in His presence (Ex. 24:11), they all did so. But in addition to Moses and the seventy were also Aaron, and Nadab and Abihu, the sons of Aaron who would later perish.
It says that these men saw God, and did eat and drink. And then they went down the mountain, went on with their lives, which ended badly.
We may not say, without horrible contradictions, that God was somehow surprised by how Nadab and Abihu ended their lives. God is God, and knows the end from the beginning. But neither may we say that Nabab and Abihu were not really on the mountain, that they did not really eat and drink, and that they did not really see God. They did all these things. Apostasy is a real sin, committed by real people. It is not a sin committed by those set apart in the love of the Father before the foundation of the world, but it is a sin committed by visible and real members of His covenant people.
But we are not told to sort out the eternal decrees in order to determine who may come to the Table. Rather, the Table (along with other means of grace like the preaching of the gospel) sorts out the people of God. Because Judas partook, he was driven away the way he was. Because Nadab and Abihu partook, their lives ended the way they did.
As we come, therefore, we should be filled with fear, awe, and trembling. For those who love Christ, this is not inconsistent with love, joy, and peace.