The Bible tells us what faith is, Hebrews 11:1 says, “Now faith is the substance of things hoped for, the evidence of things not seen.”
The phrase “hoped for” does not imply a mere wishful thinking it indicates a confident expectation; the kind of confidence we have when we have a good reason to believe something. Faith is not blind but is strongly warranted confidence – you know that you know!
Faith is having confidence in something you have not experienced with your senses. It’s not the act of “believing without a reason.” Biblical faith is the act of believing in something unseen for which we do have a good reason.
For example, “By faith Noah, being warned of God of things not seen as yet, moved with fear, prepared an ark to the saving of his house; by the which he condemned the world, and became heir of the righteousness which is by faith.” Hebrews 11:7
When we believe that God will keep a promise, this constitutes faith because we cannot “see” it and yet we have a good reason for it: God has demonstrated that He keeps His promises.
Listen to this, “By faith Abraham, when he was called to go out into a place which he should after receive for an inheritance, obeyed; and he went out, not knowing whither he went.” Hebrews 11:8
Reason is a tool that God has given us that allows us to draw conclusions and inferences from other information, such as the information He has given us in His Word. Reason is an essential part of Christianity; God tells us to reason (Isaiah 1:18) as the apostle Paul did (Acts 17:17).
In fact, many people have misunderstandings of faith, as they also have misunderstandings of reason. I could not know that I am saved apart from using reason. God tells us to reason (Isaiah 1:18). We are to have a good reason for what we believe, and we are to be always ready to share that reason with other people (1 Peter 3:15). So we attempt to show unbelievers that our belief in the Scriptures is reasonable, justified, and logically defensible. This is perfectly appropriate and is the kind of reasoning God expects us to use. We are to reason from the principles of God’s Word.