In a word, just as the most perfect love in the angels and blessed in heaven springs from the constant contemplation of God, so all perfection and holiness of life amongst men on earth comes from comes from the constant recollection of the presence of God; nay, we might say that the perfect observance of this practice and the attainment of perfection are one and the same thing. When the Lord God chose Abraham as a model for the whole world, He told him in a few words what he had to do: “Walk before Me and be perfect.” That is, according to the Septuagint, always remember My presence, and you will surely attain perfection.
In the lives of the Fathers we read that a certain monk went to St. Antony, and spoke to him thus: Father, what shall I do that will give most pleasure to God, so that I may attain that perfection which Our Lord requires of us in the Gospel? The monk thought that the Saint would give him a number of rules and instructions; but Antony, skilful teacher of holiness as he was, who had passed many years in the practice of all virtues, gave him simply this admonition: “Wherever you go, keep God always before your eyes.” For he knew well that this was the shortest road to Christian perfection.
St. Teresa says of herself, as we read in the fourth book of her Life, that she always strove with all her might to walk in the presence of God, and she thus made such progress that she is still looked on as a miracle of holiness. Amongst other lessons she has left us is this: that we should always act as if we saw the Almighty God standing beside us; and if we observe that, we may be sure of deriving the greatest advantage for our souls. Nor was it merely during her life-time on earth that the holy virgin recommended that practice, for she appeared after her death to some religious of her Order, and assured them that, if they wished to attain perfection, they should always observe it.
Fr. Francis Hunolt - The Good Christian