look like a Psalms?

"In Give Praise to God on page 67, there is a section explaining "We are to sing the Bible" in the opinion of Johnson he explains that a Christian worship song should look like a Psalms. What does he mean by it having to look like a Psalms? He does explain that if they look like a Psalms then they will develop themes and be rich in theological and experiential content but I don't understand when he says it should look like a Psalms.