This is almost exactly the same as with the one poem that I composed today. But at other times, I've also found it very useful to just collect ideas, metaphors, idioms, phrases, etc and save them for possible future use. Sometimes the ideas need to develop over greater period of time, and perhaps writing them down can even make it a tiny bit more likely that I'll notice the connections to other ideas that may come up later.
I try to do this as well. Although I do allow for a bit of poetic license and creative exploration. Some ideas may be such that I'm comfortable with writing them into poems but not necessarily into a theology book (if I ever write theology books, which is doubtful but not out of the question, I guess).
It's easy to relate to this as in some ways I might even feel a bit silly writing poems about anything other than God and his wonderful love as expressed in Christ's work on our behalf. Poems about regular human romantic love, etc. probably wouldn't seem so appropriate or personally felt. Although who knows, perhaps I'll learn to write them too someday. And there's also the proper compromise of sorts, namely, poems about romantic love as a metaphor for God's love for us. There is a Biblical precedent for this after all. Also, I've heard that Søren Kierkegaard had some kind of a metaphorical story about a king who fell in love with a peasant girl and became a peasant himself. I haven't looked that up in the original source, but something along those lines could work as a framework for even a whole series of poems.