Why can't we know for sure whether someone is saved?

Les explains that in this age of grace, the valid baptism is the one human hands cannot touch, and a lost person can have no part in it. With water baptism, however, we can never be sure as to a person’s salvation. He notes that he was brought up in a congregation where candidates for baptism were examined thoroughly, yet he later concluded that no group of men, pastors, or ecclesiastics can truly determine a person’s salvation. We can hear a testimony and come to human conclusions, but we cannot look on the heart; only God Himself can do that. Les told his class that, hypothetically, if we got to glory, we might realize some people were there whom we did not think would be, and some were not there whom we thought should be. But that will not be the case, because we will not have that kind of knowledge. We can look at someone’s outward veneer and form a conclusion, but that is not the heart. This is why Scripture says, “Judge not.” We cannot judge whether a person is a child of God; only God knows.