"Why must we worry about judging between what's true and what's false? Isn't everything by faith? What is faith anyway?"
Remember that faith does not preclude us worshiping God in spirit and in truth (John 4:23-24). And truth is something which can/must be tested (1Thess 5:21).
EITHER a personal God exists OR He does not - which is true?
EITHER God is Love OR He is not - which is true?
EITHER Jesus was resurrected OR He stayed dead - which is true?
So remember that when it comes to propositions/doctrines about the nature of God, the 'ways' of salvation, what God allows and disallows, etc. we are always dealing with truth. And the only way we can 'find out' what is true and what isn't is by examining the Bible, because we believe that it is in His word that God has revealed His truth to us.
Therefore we must be responsible to uphold the truth of what God teaches, and this may often mean evaluating (and possible 'exposing') the various doctrines and teachings circulated in our world today. We must emulate the wonderful Bereans who 'examined the Scriptures everyday to see if what Paul said was true' (Acts 17:11).
But back to 'faith' - what is it?
Faith - to plagiarize Scripture - is when we are certain of God despite not having seen Him (Heb 11:1). Faith is also when we orient our lives around the truth(!) of God's Word and His love despite not having witnessed the goal to which faith points (see the 'hall of heroes' in Heb 11 itself).
Yet what does all this have to do with truth? 1Cor 15:14-17 states, "If Christ has NOT been raised, our preaching is useless and so is your faith...your faith is futile". This means that our faith in Jesus is ultimately centered and completely dependent upon the truth of His resurrection which is also the climax and fulfilment of every other truth of God.
Faith is truth made personal and life-changing. It is when we take the truth that we know and 'apply' it in and to our lives. Faith involves a personal decision to act upon this truth and realign our lives around it even though we ourselves have not seen the physical Christ. When we do all of this undeterred by evidence to the contrary.
When we say we 'have faith in' God, we are basically committing ourselves to behaving AS IF God exists, AS IF He loves us, AS IF He will keep His promises, AS IF He'll take care of us, AS IF His commands reflect His goals and priorities for us, etc. and we do all this despite His invisibility and apparent 'silence'.
In a word, faith goes 'beyond' truth. It's when we TRUST a person based on his/her CHARACTER and then proceed to ACT upon this trust. (James 2:18-19 gives us a sober warning against 'action-less faith'). Truth is purely cognitive, intellectual, 'factual', etc. One may know all truths and stop there. But faith involves decision, commitment and 'risk' towards truth.
One way of illustrating the faith/truth interaction is the following example where Jack has promised to fetch Jill at approx. 8.00p.m. Questions of truth arising would include:
Still, EVEN THOUGH all the above questions may be answered in the affirmative, Jill still has to make a personal decision of faith in Jack which will go 'beyond' the truth issues brought up: Can I TRUST him to pick me up at the appointed time?? This trust, as all of us should know, would be strengthened if Jill has a good personal relationship with Jack and he's come through on most (if not all) of his promises. Notice that even if Jack CAN be trusted, Jill's faith MAY still be uncertain if she doesn't know him well enough or has an attitude of skeptism towards him or guys in general(!), *grin*.
Alright, but given that Jill has DECIDED to trust Jack, what would her
'faith' in him look like? The answer, as we have already suggested above,
is to behave AS IF he will pick her up on time! She will (among other
things):
i. Wait patiently without anxiety
ii. Not be too desperate in planning a 'back-up' or alternative transportation
(especially one which she knows will hurt Jack's feelings)
We can see our relationship with God somewhat mirrored by this example. For when we trust God with our hearts and our lives, we can have 'peace in our hearts' (no need for anxiety, Phil 4:6) and not have to rely on 'other gods' (money, power, etc.).
In fact, given that Jill doesn't need to worry about Jack coming on
time, she can even focus her energies on performing her other house chores
or responsibilities (or even prepare a gift for Jack, *smile*). And this
is PRECISELY what God wants our faith to be like: To focus on seeking His
Heart and His Kingdom, loving and serving people and to do so WITHOUT being
overly concerned or 'bogged down' regarding our existential needs. Nevertheless
we are still responsible to make sure we expound and guard the - again
- revealed truth of His Word, upon which our love for Him must stand.
Hope this helps,
Alwyn