When the Bible speaks of faith, it speaks of it in two ways.
1) "The Faith" - the faith that is to be believed - the objective truth about who Jesus is and what He has done - also called the Creed.
2) "your faith" - the faith which believes - the subjective trust that a believer has in The Faith (Jesus).
In other words, God has revealed "The Faith," and calls for "your faith" in it.
BUT... something has become terribly messed up these days. People only ever talk about #2, as though it is what really matters. There is a teaching which says "As long as you have faith" - "My faith kept me strong" - "Just believe" - but these cheesy clichés can be said by anyone about anything. They are found in Disney. They are the slogan for our Olympic team. They are found printed on rocks and sold in trinket shops. So let me say this plainly.
"Your faith" is NOTHING - if it is placed in the wrong thing. Faith is not powerful. It is not strong. It is merely what holds onto something else, and if that thing is not "The Faith" - "your faith" is worthless.
Put another way, we should not ask people "Do you believe?" - but "What do you believe?" It doesn't matter if someone believes in God, if all they mean is that He exists. What matters is that they believe that when they were dead in their sins and hopeless, Jesus was crucified in their place and having risen from the dead promises them eternal life with Him.
So, let's apply this to God's Word. God tells us His Word is clear and that we are able to believe, teach and confess it in its purity. However, there are many different interpretations of the Bible. And all of the people who hold to these interpretations, believe in them with equal strength. But "their faith" does not make their interpretation true. God's people have been mixing His truth with falsehood since the Fall. It is the most noticeable thing about God's people in every narrative of the Scriptures. God is able to save them despite their falsehood, but He does not want them mixing things up in this way.
So what does this mean? According to the 1st, 2nd and 3rd commandments, the chief thing the Christian is concerned about in their relationship with God - is that His Name - His Word - is kept pure. The Christian desires pure doctrine above all things, because the only way God reveals Himself to His people is in His Word - His doctrine. When you get doctrine wrong, you don't have God, you have the Evil One.
The beginning of the Lord's Prayer shows this also. Hallowed be thy Name (Your teaching). Thy kingdom come (Your Word of power). Thy Will be done (that I might trust in Your Son revealed in Your Word).
This is a joy for the Christian. It means we are pushed back into God's Word all the time to see what is in accordance with it.
Lord, keep us steadfast in Your Word
Curb those who by deceit or sword
Would wrest the kingdom from Your Son
And bring to naught all He has done