If the Scriptures alone where enough, the Scribes and Pharisees would have been Christians when Jesus got here.
Jesus Christ preached "the Law of Moses and the Prophets and the Psalms." The Pharisees were locked in their human traditions. This invalidates your statement:
Matthew 15:
Then came to Jesus scribes and Pharisees, which were of Jerusalem, saying,
2 Why do thy disciples transgress the tradition of the elders? for they wash not their hands when they eat bread.
3 But he answered and said unto them,Why do ye also transgress the commandment of God by your tradition?
4 For God commanded, saying, Honour thy father and mother: and, He that curseth father or mother, let him die the death.
5 But ye say, Whosoever shall say to his father or his mother, It is a gift, by whatsoever thou mightest be profited by me;
6 And honour not his father or his mother, he shall be free. Thus have ye made the commandment of God of none effect by your tradition.
7 Ye hypocrites, well did Esaias prophesy of you, saying,
8 This people draweth nigh unto me with their mouth, and honoureth me with their lips; but their heart is far from me.
9 But in vain they do worship me, teaching for doctrines the commandments of men.