There are some verses in the NT that mention belief in the process of salvation. (e.g. Acts 16:30-33). On the other hand, if belief is required for salvation, then several problems are created:
(1) Is belief a choice or a response to evidence?
(2) Is belief a human work or a gift of grace from God?
(3) How much belief is required for salvation? Are you really saved?
Maybe we can eliminate these problems by assuming universal salvation. The "good news" to be preached is universal salvation. The role of belief is to give people the necessary hope to begin living more righteous lives. This is why people believe and are then baptized.
So can you find some quotes from the Bible or other early Christian writings to show this idea is wrong?
I'll attempt to respond both as a Lutheran, and also attempt to parse a more broadly Christian outlook on the subject of salvation.
1) It's important I think to establish whether by belief we mean it as a synonym for faith, or if we mean something like particular beliefs. The New Testament speaks of faith, specifically faith in and upon Christ, more than specific beliefs about Jesus this faith is trust, trusting in and upon Christ. For St. Paul it is faith which clings to Christ and which constitutes our being saved. It's not a formulaic "Believe these particular theological propositions and God rewards you with salvation", but rather instead God's salvation of the world is found in and because of Christ. Christ actually is the Savior of the whole world, and we are being saved through our faith, that is, trust in and upon the Christ who saves.
2) For Lutherans the answer can only be that faith is a gift, it is--we say--extra nos, from outside ourselves. Faith doesn't arise from within myself or from my will, it is instead granted to us, created in us, by God, it is grace. To this end we point to Ephesians ch. 2, particularly verses 8 and 9 that we are saved by grace through faith, and this faith is a gift, not of ourselves. Salvation and the faith we receive from God is not from ourselves, not by our works or efforts, but from God alone, thus nobody can boast.
3) Faith isn't quantified. When it comes to that bold, radical trust in God's grace (as phrased by Martin Luther), it being a gracious gift from God from outside ourselves, there is no specific quantity of faith, faith is faith. Faith trusts and hopes in Christ. Whether that faith is seemingly small or great, it is the same faith. The faith of very young child and the faith of the old and learned theologian is the same faith. We can be confident of our salvation not on account of how seemingly great or small our faith is, or because of anything we think, feel, say, do, or of the specific things we believe; rather we can be confident because of the sure and faithful promises of God which are found in His Word and Sacraments. I heart the Gospel, which tells me Christ is my Savior, and it is most certainly true; when the words of forgiveness are proclaimed I can confidently say my sins are forgiven by the sure and certain Word of Christ; I can boldly confess that I am a born again child of God because of the promises God has made in my baptism; and when I receive the bread and wine of Christ's Supper I have Christ's promise that it is His very body and blood broken and shed
for me. It's not me that matters, but Christ. I am a fickle, fragile, faulty, sinful person whose spiritual and religious devotion is, at any given time, in flux and who tries harder to be faithful some days more than others, who goes through the same doubts, struggles, sins, and foibles all people go through. So it can never be about me and my faithfulness, or my personal piety, or my works, or efforts. It must always go back to Christ, Christ alone, in whom alone is my hope and my salvation.
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As far as the topic of universal salvation goes. This is a lot more complex. For example such a phrase can mean a number of things. I'd argue that the traditional and historical position, one which Lutherans, Catholics, and Orthodox (as just examples) would agree to is that that God's salvation absolutely
is universal. What Christ did He did for the whole world, on the cross Christ died for the sins of the whole world, Christ died for the sins of everyone, and therefore every sin is forgiven. To that end everyone, yes absolutely everyone, has been saved once and for all by the universal work of Christ's atonement, His death and resurrection. Where the question goes from there is largely a matter of our participation, or our being brought into, Christ's universal work of redemption and salvation. The healing salve can only mend a wound if it is applied to the wound itself, and so the universal salve and salvation must now be applied to us as individuals, and to this end the Church has been tasked with bringing the saving Word of Christ to the nations, the preaching of the Gospel which is itself efficacious, and to administer the Sacraments. Christ's work for the world is administered through the ministry of His Church which has been tasked to preach and to baptize. The Church is, in the words of St. Augustine, the hospital for sinners where the treatment is administered to us and we can receive the healing and medicine we need.
But perhaps what is more commonly intended by the concept of "universal salvation" is instead what is known as Universalism, the dogmatic position that everyone will ultimately be saved and reconciled to God in the end. The Church's historic position on this issue is that Universalism, because of its dogmatism, cannot be accepted; that doesn't mean it is impossible that all will ultimately be saved, the Church has long hoped for, prayed for, that this be the case. But that we can say, dogmatically, what will be the ultimate state of things is to speak beyond what we can know or say as the Church since God has not seen fit to reveal such things to us. We must, at the end of the day, humbly concede that God alone is judge and the only One fit to be judge, and that He alone decides who is "in" and who is "out"; the Church's job isn't to speculate on such issues, but instead to be the living, serving, body of Christ in and to the world active in the continued ministry of Christ for the world, preaching His Gospel, baptizing, preaching forgiveness, feeding the hungry, etc. Christ is the Great Physician, we, as the Church, must recognize that we are but beggars, sinners, and patients even as we seek to serve as He commands. He is Lord, not we.
-CryptoLutheran
I've had some pets I think were saints
. One who risked her life for me, and warn me about rattlesnakes in our walks and I hadn't even raised her. 
