The question's as old as Job, if not older. Jacob wrestled with an angel, and limped for the rest of his life as a reminder. At least Moses saw God's back. But for Job, there was a great absence: where was God when he needed him?

At times, this sense of absence provokes a profoundly emotional crisis. We're desperate for God to reveal himself, and he doesn't. At other times, it's a philosophical conundrum: an intellectual struggle, but none the less profound for that.

According to Tom Price, a lecturer for the Oxford Centre for Christian Apologetics, it's a reasonable question. Speaking at Spring Harvest in Minehead, he asked: "Why is the evidence for God's existence so slender? Why doesn't God show himself more clearly? If belief in God is tied up with human fulfilment, wouldn't we expect him to shown himself more clearly?"

His answer is that God's existence is obvious – for a given value of the word. He distinguishes between two meanings. God's existence is obvious in the sense that it's clear and easily understandable. But it isn't 'forcefully obvious' – God does not thrust himself on our attention unavoidably and painfully, like a brick wall that we walk into.

According to Price, the fundamental issue is one of human freedom – and at the root of that is the kind of relationship that God wants with us. He isn't, for instance, primarily a moral lawgiver, a "cosmic speed camera – you're trying to live the best life you can and God is warning you when you go wrong".

Neither is he primarily an object of belief, wanting people to focus on believing the right things about him and signing up to the right statement of faith – and neither is he interested in us simply feeling good things toward him. Rather, God wants a genuine relationship in which people freely choose to know him.

So, he asks: "How could God communicate his desire to love you in a way that leaves you completely free afterwards?"

He answers: "If every day you had some irrefutable rational proof that he exists, that takes away your freedom not to believe. You can't internally reflect and say, I need you."

He quotes the 17th century French philosopher Blaise Pascal, who wrote: "God wishes to move our hearts rather than our minds. Perfect clarity (if God were completely obvious) would help the mind but harm the will. God needs us to humble our wills, so that he can have relationship with us." Pascal also said: "There's enough light for those who desire to see, but enough darkness for those who don't."

So becoming or being a Christian is not just an intellectual assent to a particular truth. It means, says Price, "giving up believing we're good enough without God's help. Giving up chasing him and trying to have the right experience. It means turning toward God, asking him to forgive you and help you. It's a grace-based relationship."

In his approach to defending the faith, Price wants to engage the heart and the head. Speaking to Christian Today, he said: "I think people are hungry for an answer that is intellectually sharp, but emotionally and relationally sensitive. If Christians present their answers in a confrontational, or aggressive way then people sense this and are not attracted to it. It feels angry and insecure.

"If we simply engage people and don't spend time talking through their worldview, we might find that they are left completely cold, as we explain truths and reasons that move others deeply. We must help people to think though their deeper worldview – quite often apologetics questions really come down to personal creeds or ways that we deal with hurt, or worries about the nature of God – and so the evangelist must have a broader toolkit than simply philosophical argument.

"We mustn't chuck philosophy and argument away, but win people through it, and invite them to explore the often more personal issues that may lie at the root of their difficulties with trusting Christ."