In an attempt to make Christianity look stupid, many atheists like to define faith as "belief without evidence", or even "belief in spite of evidence", and so Christianity, by definition, is not rational. They even attempt to prove that the Bible agrees. The number one proof verse they cite? Hebrews 11:1; "Now faith is the substance of things hoped for, the evidence of things not seen."
Does this not prove the atheist definition of faith from the Bible? Clearly, Paul wants us to blindly believe God exists without having seen Him. Right? There's a saying: "Never believe a Bible verse." The concept it is trying to describe is that you can make the Bible say just about anything if you start reading in the right place and stop reading in the right place. In many cases, it is possible to make the Bible say the exact opposite of what it says if you just read one verse.
But if you read more than just the verse being cited, which atheists seemingly never do, the context becomes clear. What we see from the rest of Hebrews is that Hebrews 11:1 has little to do with faith that God exists (although of course that is a part of it), but rather is more about faith that He will do what He has promised. Hebrews 11:1, as the reference suggests, is just the first verse of a much larger chapter. It introduces what is colloquially known as the "Hebrews Hall of Faith", which describes a number of people from Abel to Rahab before verse 32 says "For the time would fail me to tell of Gideon and Barak and Samson and Jephthah, also of David and Samuel and the prophets".
None of these people were believing without evidence. In fact, many of them had heard from God Himself. The two most prominent figures, Noah and Abraham, weren't merely believing that God exists, but that He would keep His promises. Noah hadn't just been told by a goat herder "hey, there's some dude in the sky you've never seen, and he can do all these cool magic things". No, God Himself spoke to him, and so we are told "By faith Noah, being divinely warned of things not yet seen, moved with godly fear, prepared an ark for the saving of his household" (v7).
Abraham had also been in direct, two way contact with God. Again, not believing the campfire lore of some bronze age goat herder, Abraham was personally visited by God and told that Isaac would be born to his barren wife, and was asked to sacrifice that child who had been born exactly as God had said. And so we are told "By faith Abraham obeyed..." (v8), not "by faith, Abraham blindly and naively believed".
Sarah herself had heard God's promise. She actually laughed (Genesis 18:12). And yet, in verse 11, we are told "By faith Sarah herself also received strength to conceive seed, and she bore a child when she was past the age...". Why? Not because she didn't have enough evidence to believe in the one who told her, but "...because she judged Him faithful who had promised."
Needless to say, Christianity has never been a blind faith. God never sent a revelation without sending some kind of sign that it really was from Him. In fact, another word for miracle is sign. Faith isn't the substance of things hoped for and the evidence of things not seen because it is required we believe without, or in spite of evidence. No, faith is the substance of things hoped for and the evidence of things not seen because it requires us to take what we have seen and follow it through to the conclusion about what we will see. Those in the Hebrews Hall of Faith did not know the future. Noah didn't see the post-flood world, all He saw was God saying "build an ark". Abraham didn't see his innumerable offspring, or the world's nations being blessed through him. He just heard God saying "your wife will have a child". Moses didn't see the promised land, he just heard God saying "tell Pharaoh to let my people go." Peter and the other Apostles didn't see Heaven, they just saw the risen Lord saying "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you". (Matthew 28:19-20).
Point made? I think so. Faith is not belief without evidence, but merely extrapolating the evidence we have. The ironic thing is the atheists who claim that faith is belief without evidence also have faith of all three definitions. They hope for things they have not seen, they believe things for which they have no evidence, and they believe things in spite of the evidence. By atheistic definition, it takes no faith to be a Christian, and nothing but faith to be an atheist.