--I think it was Christ who said it first..."I am the way, the truth, and the light..."
--The Deposit of Truth was begun by the Apostles, to whom Christ gave His authority on Earth, and the Apostles passed it to their followers, etc. The Deposit of Truth means that, while all that is in the Bible is inspired by God, not all that is inspired by God is in the Bible. The Church, then, led by the Holy Spirit, turns to the Scriptures AND to Tradition, as given to us by Christ and the Apostles, and speaks with Authority about matters of faith. Who is the Authority in Protestantism? There are 30,000+ denominations, so you can't say that the Bible is the only authority, as every sect has a different interpretation of it.
--Lying teachers means that those who are not of God will not stand. The "speedy doom" comes to those who oppose God, or speak about/of Christ in ways that are not OF Christ.