I mentioned earlier that people will leave a gathering with the songs you have written on their lips. Worship songs are an aid to the spiritual discipline of meditation because of their repetitive nature. Make sure that people meditate on truth-based lyrics. The former includes those songs that primarily deal only from an emotional base to the Lord. Some songs get so much in the realm of feelings that biblical truth gets sacrificed.
Metaphorical songs are songs which employ a lot of figurative language.
Many of these are solidly grounded in scripture. Some are just plain out there and invoke visualizations that can't be found anywhere in scripture. Now that I have given you some suggestions about what to shoot for when you craft your song, I will let you in on a little secret that most songwriters share. Your most powerful songs will arrive spontaneously in a matter of minutes and require only a little refinement and crafting after the initial moment of inspiration. This has been true with the songs I have written.