Participation

One possible reason people why people find belief in God unreasonable is related to their understanding of the nature of God.

Deist understanding of God

Deists accept God as creator of creation. God is transcendent but unconcerned and uninvolved in his creation. A common analogy is of God as a watchmaker. God creates and sets creation in motion (as one would wind up a watch -- if anyone still winds a watch these days -- or winds up a toy), but the existence of creation is now independent of God. That is, in the universe of all being, God, creation, and all creature stand side by side. I think this understanding of God is ultimately untenable, and makes belief in the Trinitarian Son of God becoming incarnate very difficult. How would God enter into and move within his creation? The huge problem with this understanding of God is that it puts limits on God who is infinite.

St. Thomas Aquinas argued that the essence of God is existence. That is the nature of God is existence itself or that there is no division between God's nature and his existence. In Aristotelian terms God is pure act, lacking any potential. God simply Is.

A Trinitarian Theistic understanding of God and creation

In the figure above, creation is not apart from God. God is both transcendent and immanent. Of course there are problems with graphical representations of God (indeed, trying to express the nature of an infinite God with limited human words and concepts is fraught with difficulties). Putting the green dot representing creation within God might lead someone to think that I'm saying that creation is a part of God. Creation is distinct from God, not part of God, but participating or sharing God's to-be or being. (Additionally, the graphical representation of the Trinity might lead someone to think that each person, Father, Son, and Holy Spirit are pieces of the whole God. Rather the Father is God, the Son is God, and the Holy Spirit is God. The shield of the Trinity is a better, but still limited, way of representing the Trinity)

I did a presentation trying to explain this participation for my local Bible study group. Here are the notes with graphical slides of that talk.