Stephen reminds the Jews that prophets are always persecuted. This is true. Being persecuted is an essential part of being a prophet. A prophet who was welcomed easily by the world would not be a prophet at all. A prophet faces resistance because they tell the world what the world does not want to hear. The world resists the prophet for two reasons: first, because they do not want to hear the message and second, because they do not know that he is a true prophet.
Discerning whether a prophet is a true prophet is very difficult. We are told to stay faithful to what was handed down to us. If a prophet comes and tells us something new, how are we supposed to know whether we should resist it and stay faithful or accept the new interpretation? Many voices are pretending to be prophets, telling us to ignore some part of the faith, often a moral teaching. This call for us to abandon what was handed on may even be phrased as if it were a new interpretation from God.
How could the Jews have known that when Stephen said that there was no need anymore for animal sacrifices, he was teaching the teaching of God? Jesus Christ was the final sacrifice; he offers himself forever to the Father. We know this, but the Jews did not. They knew the teaching of Moses, and Stephen was teaching that the sacrifices of Moses were now complete. We should disagree with their decision to kill Stephen, but we can sympathize with their conundrum. If Stephen were lying, they should ignore him, no matter how convincing he seemed.
The Jews in the Gospel suggest a test of Jesus to see whether he really is from God. They ask for a sign. Jesus had already given them many signs, but false prophets often perform false miracles. We know, for Jesus has told us so. Real, solid faith comes from God alone. Nothing will ever convince us if we begin by doubting God. Faith is a gift from God.
All true prophets are send by God. If a person does not know God in prayer and righteousness, they ought not expect to recognize a prophet. There is no need for us to be gullible people; we do not need to trust anyone peddling the latest crackpot theory. If someone is truly a prophet, God will tell us, but for our part, we must be listening.