How do you choose antiphons? (page o-62ff in Treasury of Daily Prayer)
(for my non-liturgical friends, an antiphon is a verse of Scripture repeated at the beginning and end of a psalm or other liturgical texts.)
I usually let the date decide it this way - I divide the date by the number of antiphons for the season. For instance, there are three for Lent, so tomorrow, 10 divided by 3 has a remainder of 1, so I'll be using #1, Matthew 4:4. Today has no remainder, so I used #3, Isaiah 53:7, 6.
(I have also divided Lent into thirds, the first third using #1, second third 2, and third third 3.)
Sometimes, like today, this somewhat random way of choosing antiphons leads to interesting results. Isaiah 53 is very solemn and somber, but Psalm 105:5-11 is rather joyous in tone - doesn't seem to go together. Yet there is this connection - The same Lord who faithfully kept His covenant with Abraham, Isaac, and Jacob has now cut His covenant with us in the blood of His Son. He promises that He has laid all our iniquity upon Christ, that "To you I will give [Heaven] as your portion for an inheritance," and He will not go back on His Word.
So, how do you choose an antiphon?