One of the standard criticisms some people have when it comes to what to do on Sunday is to say 'I don't need to go to church in order to be spiritual'. Others take things a few steps further by claiming that religion is bad, but spirituality is good. Religion hates and kills people, but spirituality enlightens. Religion is dangerous; after all, didn't fundamentalist religious people blow up the World Trade Center?

To this way of thinking Paul Tillich, in a great little book published in 1959 titled 'Theology of Culture', said, one cannot reject religion with ultimate seriousness, because ultimate seriousness, or the state of being ultimately concerned, is itself religious. Religion is the substance, the ground, the depth of man's spiritual life. This is the religious aspect of the human spirit…Religion opens up the depth of man's spiritual life which is usually covered by the dust of our daily life and the noise of our secular work. It gives us the experience of the Holy, of something which is untouchable, awe-inspiring, an ultimate meaning, the source of ultimate courage.

To have strong beliefs and opinions and to hold to them passionately is to be religious, regardless of what those ultimate concerns actually are. Thus, an ardent atheist would be religious-practicing his or her atheism religiously.

When I was going to seminary, Paul Tillich was regarded with disdain by my professors. So, of course, we students fell in line and held him in disdain as well. We picked apart his liberalisms. Paul Tillich was of that brand of theologian known as Neo-orthodox. These people found difficulties in the Bible and orthodox doctrine, but they could not altogether abandon either one.

So, they restructured things so that they could have their cake and eat it too – so that they could remain scholarly respectful, intellectually blameless, but still reverential and holders of traditional faith.

Now when I read Tillich, I find a lot to throw away; there are just better things to read. However, there's a lot of good there too. He's not a simple man. Aside from the book I mentioned already, I also like his 'Dynamics of Faith' (1957).

And I guess this is the point: Christianity has been described as a simple faith, but it's not simplistic. To be a Christian in this world requires that a person struggle through the most difficult passages in life. More than that, it requires that a person think about what he or she believes. Tillich was a complex thinker. Some might read him and say he was 'deep', while others would say he was 'opaque', meaning that they could not penetrate to the points of what he was talking about enough to hold much together and make reading him worth spit. Fair enough.

However, there are authors Christian people would do well to read. If you never challenge your body in a physical work out, you never put on muscle and grow. Likewise, if you never challenge your mind as a Christian, you never expand your vision and appreciation of God. So, who could I recommend that you read? (No, I won't start with Paul Tillich.)

I recommend people read C.S. Lewis. 'Surprised by Joy' is his autobiographical description of how he came to believe in God; that's a good place to start. Then, I would recommend the 'Pilgrim's Regress', which is an allegory of the Christian life, and of course 'The Screwtape Letters', and 'Mere Christianity'. If you want something that captures Lewis's genius for apologetics, try 'God in the Dock'.

I recommend people read a wonderful little book by Daniel Taylor, titled 'The Myth of Certainty: The Reflective Christian & the Risk of Commitment'. It illustrates how an inquiring mind exercises faith to accommodate uncertainty.

I recommend three books by Dallas Willard, who teaches philosophy at the University of Southern California: 'The Spirit of the Disciplines', 'The Divine Conspiracy', and 'Hearing God'. The first describes the disciplines of life that Jesus practice, the second is an explication of the Sermon on the Mount and a call to living in God's Kingdom now, and the third is a nice description of how to have a conversational relationship with God.

I recommend, if you want to really challenge yourself, 'Divine Discourse: Philosophical Reflections on the Claim that God Speaks', by Nicholas Wolterstorff. Glenn Pettigrove, writing a review at Amazon, said of this book, 'divine discourse is a philosophical and theological treat. It offers a philosophical exploration of the devotional reading of scripture.

In so doing, it unveils the conceptual, epistemic and interpretive obstacles that one faces if one believes that God spoke and perhaps continues to speak through sacred texts'.

I recommend 'Knowing God', by J.I. Packer. He talks of the difference between knowing things about God and knowing God Himself-directly and experientially. A book very much similar to this is 'True Spirituality', by Francis Schaeffer.

Read these books. Read these kinds of books. Read them religiously. Think on them. Let them disturb you. Let them inform you. Let them inspire you. Listen for the voice of God between the lines, and let that kind of religion expand your spirituality.