Tradition

If is important to understand that nothing in Tradition contradicts Scripture.

The early church was very careful to guard against heresy. This is why we can see evidence in the Bible of writings that corrected churches that were going in the "wrong" direction. The Bible also tells us of the necessity of keeping tradition. These are not the traditions of men that Christ warns against but apostolic traditions:

1 Corinthians 11:2 (NAS)
Now I praise you because you remember me in everything and hold firmly to the traditions, just as I delivered them to you.

2 Thess 2:15 (NAS)
So then, brethren, stand firm and hold to the traditions which you were taught, whether by word of mouth or by letter from us.

2 Thess 3:6 (NAS)
Now we command you, brethren, in the name of our Lord Jesus Christ, that you keep away from every brother who leads an unruly life and not according to the tradition which you received from us.

To ensure that apostolic tradition would be passed down, Paul said to Timothy, “The things which you have heard from me in the presence of many witnesses, entrust these to faithful men who will be able to teach others also. " (2 Timothy 2:2)

Christ himself promised that the gates of Hades would not prevail against His church:

Matthew 16:18
I also say to you that you are Peter, and upon this rock I will build My church; and the gates of Hades will not overpower it.

It is well established that the Catholic Church has its roots at the time of Christ. They have documented succession from the apostles. They were the only church (outside of the Orthodox church 1054 AD) for 1500 years until the Reformation. So, we have to ask ourselves. Did the early church screw it up? Or did Christ keep his promise to protect his church? Some claim that there was a "remnant" of truth (a protestant-type Christianity) that was "underground" and finally emerged at the Reformation, but there is not one shred of evidence for this, secular or otherwise. Also, Christ did not promise to protect a "remnant".

Christ established a visible Church... the Church is more than just the invisible body of Christ. He also gave His Church authority. For Protestants, their authority is the Bible alone but it is evident in the Bible that this profitable but not necessarily all-sufficient. The Church is the pillar and foundation of truth, not the Bible:

1 Timothy 3:14-15
Although I hope to come to you soon, I am writing you these instructions so that, if I am delayed, you will know how people ought to conduct themselves in God's household, which is the church of the living God, the pillar and foundation of the truth.

Matthew 18:15-17 (NIV)
"If your brother sins against you, go and show him his fault, just between the two of you. If he listens to you, you have won your brother over. But if he will not listen, take one or two others along, so that 'every matter may be established by the testimony of two or three witnesses.' If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, treat him as you would a pagan or a tax collector.

Note above that it does not say, take it to "a" church but "the" church!

For me, what this boiled down to is: Do I believe that God would want His followers to know the truth and if He did, did He do his part to protect it for the first 1500 years or did all those people die believing they had truth when they really didn't? Can I offer you some hard evidence that the early church was fully truthful? No. But I do believe that Christ kept his promise and I do believe that the writings of the early church are very Catholic in theology. I do believe that the Catholic Church has proven through its records of succession that it is the Church established by Christ.

I believe that the Holy Spirit infallibly guided men to decide which books of the Bible were considered inspired... Why then would it be impossible for the Holy Spirit to continue to guide His Church into all truth? (John 16:13)

More verses supporting Tradition:
John 21:25
Acts 20:35
2 Timothy 1:13
2 Timothy 2:2
2 Peter 1:20
2 Peter 3:15-16
Romans 10:17
1 Corinthians 15:1-2