The LORD appeared to Abraham near the great trees of Mamre while he was sitting at the entrance to his tent in the heat of the day. Genesis 18:1
In this event God tests Abraham’s heart to determine whether he is really a circumcised believer. God appears in such a commonplace way that Abraham is not aware of His identity. I’ve long wished for some kind of a test that could be used in Bible schools and seminaries to determine the degree of spiritual maturity the students have attained. All the tests that are commonly used reveal only the amount of information that a student has amassed. There is little that reveals the real spiritual achievement of a life.
Nevertheless, although humans have not been able to devise any such test, God is always testing us, and His testing does not come when we are warned and ready. Anyone can pass a test then. If I tell you that I am going to test you to see if you exhibit love under pressure, whether you can keep your temper when you are being irritated, and if you can be sweet when things are going wrong, you are likely to pass with flying colors.