Anonymous 6th century
...when you stand in prayer sign yourself with the cross, collect your thoughts to gather and prepare yourself properly; concentrate on him to whom you are praying, and take care that your thought does not depart from him until your prayer has reached its conclusion. At the very beginning of your prayer, compel yourself so that your tears flow and your mind is filled with suffering: in this way your whole prayer will gain advantage. For any prayer in which reflection on God and mental contemplation is not mingled is a mere weariness of the flesh. Take care that your mind does not wander off during the time of prayer as it thinks about empty matters: in that car, instead of arousing the Judge to reconciliation, you will stir him to anger, having been insulted by you. You are full of fear before the world's judges, but in God's presence you show contempt: if someone is not aware of where he is standing and what he is saying, how can he suppose that he is offering up prayer? No, arouse yourself and concentrate your mind at the times when you stand in prayer; your Lord is speaking with you, so do not wander off; his chosen angels surround you, so do not be perturbed; ranks of demons are standing in front of you, so do not slacken. Rather take refuge in trust in your Lord and start off on the road of prayer confidently, turning aside neither to the right nor to the left; then all of a sudden you will arrive at the pace of tranquillity which is exempt from any element of fear, and the offering of your prayer will be accepted, as was Abel's (Gen 4:4), your mind being attentive and aware: whereas the Adversary who opposes you is put to shame, for he becomes fearful of you during your tie of prayer, seeing that the words of your mouth correspond to the will of God.
Resource: The Syriac Fathers on Prayer and the Spiritual Life, pp 174-175
10 hours ago