The contemplation of God is attained in many different ways. For God is known not only when we marvel at His incomprehensible substance, that which is still hidden in the hope of promise, but we see Him also in the greatness of His creation, or by pondering upon His justice, or helped by the though of His daily providence, or when we run over in sincerity of mind the things He has done for His saints generation after generation…
Many other subjects of contemplation are there of a similar kind which will rise up in our minds, according to the holiness of our lives and the purity of our hearts, whereby they of clean vision may see or lay hold upon God. These no man will constantly retain if in him any of the carnal appetites still subsist, for the Lord saith: ‘Thou canst not see My Face, for man shall not see Me and live’ (Exodus 33:20) that is, in this world, and amid earthly affections.
~St John Cassian (Conference I, 15 with Abbot Moses)
Prayerful Life 