Eph 4:11-13 It was he who gave some to be apostles, some to be prophets, some to be evangelists, and some to be pastors and teachers, to prepare God's people for works of service, so that the body of Christ may be built up until we all reach unity in the faith and in the knowledge of the Son of God and become mature, attaining to the whole measure of the fullness of Christ.The Holy Spirit, speaking through the apostle Paul, teaches us that the maturing of the church should lead to unity in the faith. There is only one faith on which we are to build unity (vs 5). What is that faith?
Joh 3:16 "For God so loved the world that he gave his one and only Son, that whoever believes [Gk pisteuo] in him shall not perish but have eternal life.Note however that two of the above passages link salvation to faith plus something (confess Jesus is Lord; baptism). In the Romans passage, our salvation is conditional upon making a sincere and legitimate commitment to obey Jesus as Lord. In the Mark passage, salvation is made conditional upon a particular case of obedience. This is consistent with what Paul wrote in the introduction to Romans:
Rom 10:9 That if you confess with your mouth, "Jesus is Lord," and believe [Gk pisteuo] in your heart that God raised him from the dead, you will be saved.
Mar 16:16 Whoever believes [Gk pisteuo] and is baptized will be saved, but whoever does not believe [apisteo] will be condemned.
Rom 1:5 Through him and for his name's sake, we received grace and apostleship to call people from among all the Gentiles to the obedience that comes from faith.We are called to the kind of faith that produces obedience.
Rom 14:2-4 One man's faith allows him to eat everything, but another man, whose faith is weak, eats only vegetables. The man who eats everything must not look down on him who does not, and the man who does not eat everything must not condemn the man who does, for God has accepted him. Who are you to judge someone else's servant? To his own master he stands or falls. And he will stand, for the Lord is able to make him stand.Note that the two people described do not agree on what it means to obey in the case of eating meat. Each one is responsible to obey what he understands. They share the same kind of faith in Jesus, but that faith produces differences in obedience in the two men, because they have different understandings on the subject of eating meat.
Rom 14:22-23 So whatever you believe about these things keep between yourself and God. Blessed is the man who does not condemn himself by what he approves. But the man who has doubts is condemned if he eats, because his eating is not from faith; and everything that does not come from faith is sin.Either, or both, may be condemning himself by what he approves. Even so, if the two cannot come to agreement on what is required for obedience, they must not quarrel nor judge one another, but instead they must keep their convictions to themselves, and leave the matter in God's hands. (The few limited exceptions to this are spelled out in scripture; for example, 1 Cor 5:9-11 ) It is before God that each stands or falls. And God is able to make both of them stand.