"And when the day of Pentecost was fully come, they were all with one accord in one place. And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. And there appeared unto them cloven tongues like as of fire, and it sat upon each of them. And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance." - Acts 2:1-4

The disciples had become living temples of God.

"Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?" - 1 Corinthians 3:16

Jesus had placed His name upon them by water baptism.

"After these things came Jesus and his disciples into the land of Judaea; and there he tarried with them, and baptized." - John 3:22

They were with one accord, holy, living sacrifices.

"I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service." - Romans 12:1

As holy, acceptable sacrifices, Jesus consumed them with the baptism of the Holy Ghost.

"John answered, saying unto them all, I indeed baptize you with water; but one mightier than I cometh, the latchet of whose shoes I am not worthy to unloose: he shall baptize you with the Holy Ghost and with fire:" - Luke 3:16

The cloven tongues LIKE as of fire, that sat upon each of them was a reminder of the dedication of Solomon’s Temple.

"Now when Solomon had made an end of praying, the fire came down from heaven, and consumed the burnt offering and the sacrifices; and the glory of the LORD filled the house." - 2 Chronicles 7:1

"And the priests could not enter into the house of the LORD, because the glory of the LORD had filled the LORD'S house." - 2 Chronicles 7:2

"And when all the children of Israel saw how the fire came down, and the glory of the LORD upon the house, they bowed themselves with their faces to the ground upon the pavement, and worshipped, and praised the LORD, saying, For he is good; for his mercy endureth for ever." - 2 Chronicles 7:3