John Cassian (Egypt, 365-435)
This is something which has been handed on to us by some of the oldest of the Fathers and it is something which we hand on to only a very small number of the souls eager to know it:
To keep the thought of God always in your mind you must cling totally to this formula for piety: "Come to my help, O God; Lord, hurry to my rescue" [Psalm 70:1].
It is not without good reason that this verse has been chosen from the whole of Scripture as a device. It carries within it all the feelings of which human nature is capable. It can be adapted to every condition and can be usefully deployed against every temptation. It carries within it a cry of help to God in the face of every danger. It expresses the humility of a pious confession. It conveys the watchfulness born of unending worry and fear. It conveys a sense of our frailty, the assurance of being heard, the confidence in help that is always and everywhere present. Someone forever calling out to his protector is indeed very sure of having him close by. This is the voice filled with ardor of love and of charity. This is the terrified cry of someone who sees the snares of the enemy, the cry of someone besieged day and night and exclaiming that he cannot escape unless his protector comes to the rescue.
This short verse is an indomitable wall for all those struggling against the onslaught of demons. It is an impenetrable breastplate and the sturdiest of shields. Whatever the disgust, the anguish, or the gloom in our thoughts, this verse keeps us from despairing of our salvation since it reveals to us the One to whom we call, the One who sees our struggles and who is never far from those who pray to Him. If things go well for us in spirit, if there is joy in our hearts, this verse is a warning to us not to grow proud, not to get puffed up at being in a good condition which, as it demonstrates, cannot be retained without the protection of God for whose continuous and speedy help it prays. This little verse, I am saying, proves to be necessary and useful to each one of us and in all circumstances. For someone who needs help in all things is making clear that he requires the help of God not simply in hard and sad situations but equally and amid fortunate and joyful conditions. He knows that God saves us from adversity and makes our joys linger and that in neither situation can human frailty survive without His help.