He who prays must never stand still on the steep ascent that leads to God. Just as he has to progress upwards from strength to strength in the practice of the virtues (Psalm 84:5-7), and to rise in his contemplation of spiritual truths from glory to glory (Corinthians 3:18), and to pass from the letter to the spirit of Holy Scripture, so he must advance in a similar manner within the realm of prayer.
He must raise his intellect and the resolve of his soul from what is human to what is divine, so that his intellect can follow Jesus the Son of God, who has passed through the heavens (Hebrews 4:14) and who is everywhere. For He has passed through all things for us by the dispensation of His incarnation, so that we, by following Him, may pass through all that is sequent to Him and so come to be with Him, provided we apprehend Him not according to the limitations to which He accommodated Himself in His incarnation but according to the majesty of His natural infinitude.
~St Maximos the Confessor
Even if we do not wish to believe Him, it was Jesus who said that no one can serve two masters (Matthew 6:24).
~St Thalassios the Libyan