Many people have the idea that Christianity asks them to leap into the dark and swallow stuff about miracles and then for me to call it 'reasonable' - "No, give me a break!" - You might well reply. Hang in there, and we'll see if we can sort this out.
Briefly, I aim to show that something that is reasonable is quite different from it being rationalistic God. Then I will show that biblical Christianity invites careful thought - but not irrational thought. This topic falls into the category of popular apologetics.
Some basic meanings
Rationalism rests on secular foundations, thinking man is the master of the cosmos, who by his own reason will discover everything there is to know. This sort of thinking is based on naturalism, a philosophy that believes everything that exists is in the natural, physical realm where science operates.
And yes, it appeals to your reason to support denials of the supernatural. But let's be clear, those denials are not open to being checked by scientific method - rationalism is a philosophy that people are prepared to take on trust - a leap perhaps, which assumes there is no such thing as the supernatural; hardly scientific proof.
Let's now make something else clear
Reason is used by minds - that is by people who have already acquired many beliefs, and who are then inclined to reason, generally using the laws of logic, as if those beliefs were credible.
Now, here's an interesting observation made by the astute Thomas Jefferson"The moment a person forms a theory, his imagination sees in every object only the traits which favour that theory." How do we check our beliefs are not merely the way we prefer to see things? This is a very challenging question!
Are there any simple truth checks we need to apply to Christian beliefs to confirm they are both credible and reasonable, and even beyond that, are supernatural and dependable revealed truths?
Here are a few pointers:
The New Testament and early Christianity
Check into it, because it is open to be checked out for historical detail and accuracy: from Roman Governors, to provinces, to numerous places, customs, personal names, storms at sea, Jewish feast days and ceremonies, to Jesus' personal claims, his teaching, his miracles, and his death and resurrection.
Ultimately the case for Christianity stands or falls with Jesus' claims and his actual bodily resurrection. The New Testament is clear that Jesus voluntarily gave himself into death as a punishment for sin and then rose in triumph over death itself. These beliefs are the foundations of Christianity - extraordinary indeed, judged unworthy of serious credibility only to unbelief, because these events are neither irrational nor unreasonable.
The evidences for Jesus' resurrection
Before you write off Jesus' resurrection, consider some of these points. The Gospel records were written down well within living memory of the events described. If they were made up and delusionary, people would have pulled the Gospel accounts to shreds. Christianity would have been discredited as a massive hoax and we would probably never have even heard about it. However, Jesus made many direct claims that he would rise from the dead (Mark 10:34, John 10:18), but not surprisingly, his disciples responded with blank disbelief ..
When Jesus was crucified, the Roman authorities made doubly sure he was dead (John 19:33-35). In spite of which, some say he merely swooned and recovered, shaking off the tightly-wound embalming strips. This is very unlikely, not something we hear others doing. And his followers would have been most unimpressed by such a pathetic substitute, emaciated and with terrible wounds, for a real rising that Jesus has previously foretold.