Sceptics have said that faith (even though they live by faith as much as any Christian) is believing something in the absence of evidence.
I’ve said before that agnostics are the ones who could call themselves the most scientifically minded. Agnostics are the ones who only go as far as the evidence will take them. Christians and atheists, on the other hand, use inductive reasoning to take them part way, and then bring about a deductive conclusion based upon the evidence in combination with their pre-set world-view.
The Bible defines faith as, “Now faith is being sure of what we hope for, it’s the evidence of what we do not yet see.” Hebrews 11:1
In that sense Christian faith can be described as “Choosing to believe the conclusion regarding the evidence that God has placed before us.” Atheists of course say that the existence of the universe isn’t evidence of anything. It just is and it’s always been. Pfft!
On a behavioural level faith is living as though you actually believe what God says to you in His Word. There are many many people in every congregation who say they follow Jesus but they refuse to obey Him. What He says doesn’t make sense to them (eg. Love your enemies) so they do their own thing.
Faith is taking what Jesus says He will do and letting those words change the way we respond to Him and to others. Simply knowing what God says doesn’t do anything. Most atheists know what God says. satan knows what God says. True faith is shown by trusting God enough to do what He says.
“Even so faith, if it has no works, is dead, being by itself.” (James 2:17).