I’ve found the following excerpt on meditative singing from the book “Prayer For Each Day” by the monks of Taizé, to be helpful:

Singing is one of the most essential elements of worship. Short chants, repeated again and again, give it a meditative character. Using just a few words they express a basic reality of faith, quickly grasped by the mind. As the words are sung over many times, this reality gradually penetrates the whole being. Meditative singing thus becomes a way of listening to God. It allows everyone to take part in a time of prayer together and to remain together in attentive waiting on God, without having to fix the length of time too exactly.

In the Selah service, the use of meditative choruses from Taizé and others like it greatly enhance the use of traditional hymns, instrumental compositions, readings from Scripture, Celtic prayers and silent prayer.