Is faith in God and in the things of God reasonable? I mean do you believe with a reason?
Yes, certainly. Paul told Festus on Acts 26:25 that what we believe about Jesus is “true and reasonable.” Of course, this is just a statement and you should not believe it is true and reasonable just because Paul says so. You cannot “prove” the existence of God and the basic claims of Christianity in the sense of a deductive, mathematical proof. What we can all do is ask ourselves what is the most reasonable conclusion about the existence of God and the central claims of Christianity. Is it more reasonable to believe that these things are true or that they are false? This is what you are asking.
As for the existence of God, I believe that without any question the most reasonable conclusion based on the facts about the universe is that there exists a powerful, intelligent Creator that we call God. The evidence for this comes from the incredible level of design in the universe–design with the apparent purpose that intelligent living beings can exist. I could give SO MANY examples of this. Actually, I gave a talk on this subject recently and have a link for you to find this lesson. http://evidenceforchristianity.org/god-and-science-at-bakersfield-college-2/ In this lesson you will learn about the incredible number of reasons it is only reasonable to believe that there is a single, powerful, intelligent Designer and Creator of the universe. The precise nature of the physical constants which allow life to exist is just one example. Other evidence for existence of God is the fact that the universe began to exist. Everything which begins to exist is caused. That cause is God. The reality of moral absolutes is also evidence for God. Lying is wrong. Rape is wrong. Hatred is wrong. Greed is wrong. Why are these things wrong? If there is no authoritative power in the universe, then these things are not wrong. Otherwise, who says that anything is immoral?
As for Christianity itself, are the central claims of Christianity about the universe reasonable? I say yes, without a doubt. Christianity claims that the universe was created. It was. Christian belief is supported by the evidence for the resurrection. It is supported by fulfilled prophecy. It is supported by the perfect life of Jesus. There is much reason to believe that the Christian description of reality is correct. I have much to say about this and have many lessons at the web site I can recommend to you. Here is one audio you can listen to. http://evidenceforchristianity.org/what-is-truth-lesson-in-seattle/ I am attaching an article on the Christian worldview which will explain some of what I am claiming.
You are asking a really broad question, so it is hard to know if I am answering it as you need, so let me know if this is sufficient.