The Catholic Church viewed itself as having the authority to dispense salvation, thus placing its tradition on equal par with the Bible. Beginning with Martin Luther, others in his wake joined in this protest, thus beginning the birth of the “Protestant Reformation” on October 31, 1517 (called “Protestantism” since they protested against the Catholic Church on much of its theology of salvation and church practice).
In Jesus’ day the Jewish Scribes and Pharisees had developed an elaborate system of laws and rules that they viewed as on equal footing with the Old Testament. When Jesus would deal with that system, he would contrast his teaching from scripture to their system. When referencing their system, he would use the phrase: “it has been said”. (compare Matthew 5:21,27,31). However whenever He was making an authoritative statement, or quoting scripture, He would use the phrases: “but I say” or “it is written”. (Matthew 5:22,28,32)
Believing in sola scriptura or "the Bible alone" spells the only way of fidelity to the true Gospel