But the clergy always stood aloof, preferring to meet in their own houses of convocation; and the archbishops, bishops, and greater abbots only attended because they were great holders of land and important feudal lords.
Although the knights of the shire were of much the same class as the barons, the latter received personal summons to attend, and the knights joined with the representatives of the cities and boroughs.

So the two Houses of Parliament consisted of barons and bishops--lords spiritual and lords temporal--and knights and commons; and we have to-day the House of Lords and the House of Commons; the former, as in the thirteenth century, lords spiritual and temporal, the latter, representatives from counties and boroughs.
The admission of elected representatives was to move, in course of time, the centre of government from the Crown to the House of Commons; but in Edward I.'s reign Parliament was just a larger growth of the King's Council--the Council that Norman and Plantagenet kings relied on for assistance in the administration of justice and the collection of revenue.
The judges of the supreme court were always summoned to Parliament, as the law lords sit in the Upper House to-day.
Money, or rather the raising of money, was the main cause for calling a Parliament.

The clergy at first voted their own grants to the Crown in convocation, but came to agree to pay the taxes voted by Lords and Commons, And Lords and Commons, instead of making separate grants, joined in a common grant.
"And, as the bulk of the burden fell upon the Commons, they adopted a formula which placed the Commons in the foreground.

The grant was made by the Commons, with the assent of the Lords spiritual and temporal.

This formula appeared in 1395, and became the rule.