There are twin themes that wind around one another all through the Scriptures. The first is that God communicates – he speaks to us, reveals who he is, and makes himself comprehensible. The other is that he hides himself, keeps himself at a distance, and remains incomprehensible. These two ideas depend on each other, a bit like children holding hands and swinging around one another. Lose one of these, and the other will go spinning off and eventually come crashing to the ground. If God only reveals himself and meets us at our level, and is no longer 'other', then our faith simply reduces him to our level. But if he remains distant and incomprehensible, all we are left with is untestable speculation about what God might or might not be like. In fact, the wonder of his speaking to us is precisely that he is beyond our imagining, and yet makes himself known.

This is beautifully illustrated in Isaiah 55. It is a chapter all about God's communication – his invitation and his presence with those who turn to him. "Come, all who are thirsty, come to the waters (v 1)...Seek the Lord while he may be found; call on him while he is near (v 6)...my word will not return empty (v 11)..." But right in the heart of it comes a statement of precisely the opposite – a statement of God's distance, which makes these other claims and invitations all the more remarkable: "As the heavens are higher than the earth, so are my ways higher than your ways and my thoughts than your thoughts" (v 9). It is this difference that leads to God's condescending love. If we were as mighty as him, we would not compromise our dignity by stooping to love a sinful humanity.

If God's communication and his strangeness hold together, then we might expect to see this strangeness made manifest in his ultimate act of communication – the sending of Jesus. And indeed we find it right at the heart of Jesus' own teaching, though all too often we pass over it.

Both Matthew and Mark make the Parable of the Sower not just one parable among many, but programmatic within the teaching of Jesus – a parable about why Jesus tells parables. (Luke includes it, but doesn't give it the same importance.) Mark does this by putting it early in Jesus' ministry, in chapter 4 as part of just about the only extended section of teaching until we reach the 'Little Apocalypse' in Mark 13. Matthew does it by placing it in his third block of Jesus' teaching in chapter 13. And within this teaching, Jesus says at least three baffling or challenging things.

First, he draws a sharp distinction between the 'insiders' and 'outsiders'. In Matthew he just talks of 'you' and 'them' but in Mark it is even more explicit: "those on the outside" (Mark 4.11). They are excluded from insight while those on the inside have privileged access. I'm not sure we like this Jesus; he is supposed to be open and welcoming, with a particular concern for the outsider. Worse than that, his language of insider/outsider redraws the boundaries of identity and loyalty in ways we might find challenging. "These are my mother, my brothers, my sisters – whoever does the will of my Father in heaven" Matthew has just noted (12.49–50). And you don't get to choose your siblings – as some fishermen, a tax collector, a violent revolutionary and the rest of The Twelve have found out.

Secondly, Jesus then appears to be deliberately making it hard for the outsiders – he is raising the bar for them. He has come all that way, left his heavenly throne, and now he is making it difficult for people to hear and understand his message. Why would he do that? The only explanation is that Jesus is treating his listeners with dignity – he is assuming they are responsibly moral agents. They have a choice: are they going to take his teaching seriously, and want to find out more? Or are they going to choose to carry on with life as they know it? Jesus is neither going to impose his view on them (which is the problem with any universalist position), nor is he going to offer himself as an easy addition to our other interests; another hobby amongst many. To follow him means making hard decisions – the decision to grab hold of his teaching, and not allow it to be snatched away or forgotten. The decision to put our roots deep down, and not be satisfied with a superficial engagement with God. The decision to allow no other concerns or interests to crowd out our commitment. This is free grace, but it is not cheap.

Finally, Jesus adding unfairness to exclusion and challenge. "To those who have little, even what they have will be taken away." I actually think Jesus is simply describing reality here. I have just spent a week at Lee Abbey in Devon, and when there we always go to the beach and build dams, diverting the stream that flows down the beach all through the year. But the sand is quite gritty; if you try and pool the water, cutting it off from the streams flow, then the water soon drains away and you are left with nothing. But if you open it up to the stream, the water will never fail.

All this has profound implications for our understanding of faith and how we share it. Following Jesus never involves domesticating God; even as he is known by us, he always remains a mystery. And this means that sharing our faith is not about offering a bottled product, sold with a four-point formula. Instead, it is about inviting people to come and unravel a mystery. And in doing so, we don't need to offer people all the answers. Sometimes, like Jesus, we might be better off leaving people with questions – to see whether they are really interested in finding the answers.

Rev Dr Ian Paul is associate minister at St Nic's, Nottingham, and Honorary Assistant Professor at the University of Nottingham. He blogs at www.psephizo.com and tweets at @Psephizo.