The Missi of Charlemagne pressed him to declare, that all who rejected the filioque, or at least the doctrine, must be damned. All, replies the pope, are not capable of reaching the altiora mysteria qui potuerit, et non voluerit, salvus esse non potest (Collect. Concil. tom. ix. p. 277 - 286). The potuerit would leave a large loophole of salvation!