The Pause in the Psalm Verse - Explaining the same to singers

As we all know, the traditional singing of the psalms for the office provides for a generous pause after the mediant cadence (i.e., in the middle of the verse).

I know this and I teach it and I enjoy it and so do my singers. What I don't have is an explanation for it.

My interest right now comes for the desire to start dividing my singers and the hand-off between choirs is much shorter. So I'd like to be ready with an explanation.

Any suggestions, knowledge, or guesses?