Canon XVII
The Psalms are not to be joined together in the congregations, but a lesson shall intervene after every psalm.
Ancient Epitome of Canon XVII.
In time of service lessons shall be interspersed with the Psalms.
It was well to separate the Psalms by lessons when the congregation was gathered in church, and not to keep them continuously singing unbroken psalmody, lest those who had assembled might become careless through weariness.
This was an ancient custom which has been laid aside since the new order of ecclesiastical matters has been instituted. 178
Here it may be remarked we find the real reason why in our present rite, the lections, verses, etc., of the nocturns are placed between the Psalms, so as to repel weariness.