The words faith and belief in our Bibles represent the same Greek word in the original text. So when we read in Mark16:16 that “he who believes . . . will be saved” it could be written “he who faiths . . . will be saved” if there was such a word in the English language!
It is clear from this scripture that faith is our response to the Word of God read or heard; and our salvation depends on this response.
Consider Abraham, the father of all those who believe - that is, have faith: “Abraham believed (faithed) God, and it was accounted to him for righteousness” (Romans 4:3).
Faith is the characteristic that we must voluntarily manifest if we are, in God's grace, to be counted righteous. Romans 10 summarises this process:
1) It begins with “the word of faith which we (the apostles) preach” (v. 8).
2) Then must follow the voluntary response “If you confess with your mouth the Lord Jesus and believe (faith) in your heart . . . you will be saved” (v .9).
3) Thus the basis upon which we receive salvation is clearly set out “With the heart one believes (faiths) unto righteousness, and with the mouth confession is made unto salvation. For . . . ‘Whoever believes (faiths) on him shall not be put to shame’” (v.10,11).
Look how Paul gives us an example of this when in writing to Timothy he says “. . . that from childhood you have known the Holy Scriptures, which are able to make you wise for salvation through faith which is in Christ Jesus” (2 Timothy 3:15).
(Quotations are from the New King James Version of the Bible)