By St. Gregory of Sinai
We confirm that there are eight principle subjects for contemplation:
First, God, invisible and unseen; without beginning and uncreated; the First Cause of everything that exists; Triune; the one and only pre-existing Divinity;
Second, the order and rank of rational powers [the bodiless powers of heaven; the angelic world];
Third, the composition of visible things;
Fourth, the plan of the Incarnation of the Word;
Fifth, the general resurrection;
Sixth, the awesome Second Coming of Christ;
Seventh, eternal torment;
Eighth, the Kingdom of Heaven.
The first four have already been revealed and belong to the past. The last four have not yet been revealed and belong to the future, even though these four are clearly contemplated by those who, with the help of acquired Grace, attained complete purity of mind. Whosoever approaches this task of contemplation without the illumination of Grace, let him know that he is building fantasies and does not possess the art of contemplation.