Keach strongly believed that the lyrical content of a hymn should be theologically sound. Meaning that the words being sung had to contain biblical principles, thoughts, and teachings. While Keach never claimed that his hymns were inspired as the Davidic Psalms were, he believed that they worked in instructing those who sang them and committed them to memory.
The challenge left by Keach to modern hymn-writers and worship music writers at large is simple: do your lyrics read like a devotional or bible study?
Lyrics should express the beauty of Christ and the richness of His grace. In singing these kinds of songs together Keach knew that the congregation would come away from their time of singing as if they have been emerged into deep theological waters.