The resurrected and glorified Jesus Christ. If we do not believe that Jesus Christ is the head and leader of the Christian Congregation, then we are not listening to him. He said:
Matthew 23:9, 10
9 Moreover, do not call anyone your father on earth, for one is your Father, the heavenly One. 10 Neither be called leaders, for your Leader is one, the Christ.
Jesus is ALIVE. Before he ascended to heaven, he said this:
... teaching them to observe all the things I have commanded you. And look! I am with you all the days until the conclusion of the system of things.”
The Christians were to teach his disciples the things that Jesus commanded. They were also to do this:
8 But you will receive power when the holy spirit comes upon you, and you will be witnesses of me in Jerusalem, in all Ju·deʹa and Sa·marʹi·a, and to the most distant part of the earth.”
Some feel that Peter was given the headship of the Christian congregation. But that would not be the case for these reasons:
If he was so given the headship by Jesus, the apostles would not have cause to dispute over who is the greatest. But right after Matthew 16:18,on that very night, two other gospel accounts showed that they did just that. Mark 9:33-35; Luke 22:24-26
Peter's name means rock or a stone, but Jesus is the rock on which the congregation stands. Peter's name was from the masculine Greek word pe'tros. But the rock on which the congregation was built is Jesus Christ, as is clearly stated in Peter himself identified the rock-mass (the Greek word peʹtra) on which the congregation is built to be Jesus, even quoting the scriptures to establish that:
1 Peter 2:4-6
4 As you come to him, a living stone rejected by men but chosen, precious to God, 5 you yourselves as living stones are being built up into a spiritual house to be a holy priesthood, in order to offer up spiritual sacrifices acceptable to God through Jesus Christ. 6 For it says in Scripture: “Look! I am laying in Zion a chosen stone, a precious foundation cornerstone, and no one exercising faith in it will ever be disappointed.”
Peter did NOT decide on the first decision that the apostles made. After Jesus' ascension, they had to replace Judas Iscariot. The apostles consulted the scriptures which prophesied that this was to take place, then they prayed together, and two faithful disciples that were with Jesus from the beginning of his ministry were presented,.then following the scriptures, one was selected. Following Jesus' example of doing all things according to the inspired scriptures, they addressed this issue. Acts 1:13-26
When the ministry of the spirit anointed apostles resulted in several thousand getting baptized, they did not teach according to Peter, but "the teaching of the apostles." Acts 3:42
This took place every time, where the apostles behaved as a unified governing body. When there was an issue with the overlooking of Gentile widows, "the twelve" handled it, and the seven brothers presented to deal with this specific issue were brought "before the apostles" before they were assigned.
Some 15 years after Jesus' ascension, the issue of requiring Gentile Christians to be circumcised came up. Acts 15:1-3 showed that this issue was brought before the "apostles and elders in Jerusalem" indicating that by this time, it wasn't just the apostles that were in this governing body. The decision that was made after discussion and considering and applying the inspired scriptures, was sent to all Christian congregations "for observance" - they all had to abide by that decision.
Acts 16:4, 5
"As they traveled on through the cities, they would deliver to them for observance the decrees that had been decided on by the apostles and the elders who were in Jerusalem. 5 Then, indeed, the congregations continued to be made firm in the faith and to increase in number day by day."
No one else besides these brothers had deciding influence over their spiritual decisions- no kings, no emperors, no political leaders. They were not given any temporal power to enforce their decisions - brothers and sisters who were loyal to God and Jesus Christ were loyal to these brothers who strictly abided by the inspired scriptures. And the congregations were encouraged by the congregational growth that the holy spirit made possible, to cooperate with them.