For Success in Prayer You Must Attend to Yourself
You must establish the conviction that God sees and hears all, and knows all the secrets of our hearts.[1] Therefore you must attend to yourself and reject all evil; as soon as it breaks through in your thoughts or feelings, cast it out immediately, and at once repent and ask forgiveness.
(Letter 377. Vol. 3, p. 11)
You must drive away extraneous thoughts. Your prayer rule is good. Only strive always to pray from the heart; and for the heart there is this law: a contrite and humble heart God will not despise (Ps. 50:19).
Your prayer is disrupted by thoughts. Have you noticed this?! Now try to correct it. The first step toward this is: when approaching prayer, stir up in yourself the fear of God and reverence; then place your attention in the heart and from there cry out to the Lord.
And extraneous thoughts will come; as soon as you notice them, drive them away. They’ll come again, drive them away again. And so it goes. Do not allow your tongue to recite the prayer while your thoughts wander who knows where—always drive them away and pray.
You must labor and ask the Lord to help you overcome your thoughts. Do you have a collection of the fathers’ teachings on prayer?[2] Read and reflect on them, apply them to yourself. Labor tirelessly at this, and God, seeing your effort, will give you what you seek. Toil earnestly, but do not think you yourself can succeed in anything without God’s special help. Cry out to Him for it more often.
(Letter 488. Vol. 3, p. 155–156, 157)