I had hard time to understand 天人合一(健的 人神一體) until I read Christian2007 this post:
http://web.wenxuecity.com/BBSView.php?SubID=znjy&MsgID=880618
I agree that 心 is different from 靈. 天 is not the physical nature, it is 神. According to Christian2007 (if I understand it right), God gave his 靈 for human to share, and the 靈 is supposed to reside in our 心. So 天人合一 means God, and human share the same 靈. It also means, if our 心 is not pure, we don't have 靈 at all, because 靈 cannot reside in a dirty heart.
In this interpretation, 天人合一 (Our beloved tradition) is perfectly in the framework of Christianity. In my opinion, it is much clear, and it is truthful.
How we achieve a pure 心? or do we ever have a pure 心? This is another topic.