The Council of Cardinals is a special organization formed well after Tira's sacrifice to manage the expanding faith of the citizens of Galifar. The council of cardinals currently numbers fewer than one hundred, with the total membership varying based on members passing away and being inducted from the lower orders. Currently the council is composed of seventy-seven members, serving as high-level administrators and representing various orders.
Each formally recognized order is only represented by a single cardinal, but deference is usually given by cardinals from smaller orders to larger ones. Cardinals that are not representatives are usually elevated on the basis of exceptional piety and wisdom so they can fully serve the church's mission as chief administrators.
Source: Politics of Thrane
The previous three orders are largely equal in the eyes of the Church. The Council of Cardinals stands above them. Seminarians can enter the Ministers, Friars, or Templars immediately upon graduation, but only experienced and well-respected priests are promoted to the Council of Cardinals. Most Cardinals are from the Order of Ministers, with a notable few coming from the Order of Templars. Only rare individuals rise from the Order of Friars
Source: Dragonshard
Most outside the Church of the Silver Flame believe that the Council of Cardinals refers to the governing body of the Church. In truth, that body is properly entitled the Diet of Cardinals, and its members are drawn from the ranks of the Council. The Council itself is simply another order, like the others, albeit a higher one. As in any specialized profession, nomenclature helps separate the insiders from the outsiders. Scholarly pursuits are no different from religious ones in this manner.
Source: Faiths of Eberron