Pioneer Generation

God appeared to the pioneer generation of both covenants, old and new.

God appeared to the Israelites who left Egypt for Canaan under Moses.

On the morning of the third day, thunder roared and lightning flashed, and a dense cloud came down on the mountain. There was a long, loud blast from a ram’s horn, and all the people trembled. Moses led them out from the camp to meet with God, and they stood at the foot of the mountain. All of Mount Sinai was covered with smoke because the Lord had descended on it in the form of fire. The smoke billowed into the sky like smoke from a brick kiln, and the whole mountain shook violently. As the blast of the ram’s horn grew louder and louder, Moses spoke, and God thundered his reply. The Lord came down on the top of Mount Sinai and called Moses to the top of the mountain. So Moses climbed the mountain. (Exodus 19:16-20 NLT)

When the people heard the thunder and the loud blast of the ram's horn, and when they saw the flashes of lightning and the smoke billowing from the mountain, they stood at a distance, trembling with fear. And they said to Moses, "You speak to us, and we will listen. But don't let God speak directly to us, or we will die!" (Exodus 20:18-19 NLT)

The Apostles and the first generation of believers saw Jesus and witnessed His resurrection.

Jesus said to him, "Have I been with you so long, and you still do not know me, Philip? Whoever has seen me has seen the Father. How can you say, 'Show us the Father'? (John 14:9 ESV)

For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, and that he appeared to Cephas, then to the twelve. Then he appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. Then he appeared to James, then to all the apostles. Last of all, as to one untimely born, he appeared also to me. (1 Corinthians 15:3-8 ESV)

Christianity is not only about the message, but also the authentication and transmission process. After all, anyone can claim to be a prophet, but not many can descend on Mount Sinai with fire and resurrect from the dead.