So long as a doctrine is implicit in Scripture, it is appropriate to give it credence. For example, the word “Trinity” does not appear anywhere in Scripture, but its reality is certainly implicit. It is accepted by the vast majority of Christians—Catholic, Orthodox AND Protestant.
For Protestants Christianity is principally about a Book, THE Book. For Catholics Christianity is principally about a Person, the Person of Jesus Christ. He came first and taught only by word of mouth. Nowhere in Scripture do we find Him saying anything about writing anything down. But Scripture does speak of Him giving authority to His Church in the person of His apostle, Peter. His last words to His apostles are that they are to go out to the whole world and preach and baptize—word and sacrament. Catholics revere Sacred Scripture as the Word of God. But we also revere the Sacred Tradition that preceded it and, indeed, gave birth to it.
Incidentally, there is much that Luther did not reject, but that is no longer evident in the Lutheran faith. For example, Luther had devotion to Mary and believed in her immaculate conception. Even today on his tomb can be found a base-relief of her bodily assumption into heaven.
See the Catholic Encyclopedia for more on Martin Luther.
Fr. Vincent Serpa, O.P.