Eighth Letter of Brother Lawrence of the Resurrection:
You tell me nothing new. You are not the only one who is troubled with wandering thoughts. Our mind is extremely roving. But the will is mistress of all our faculties. She must recall our stray thoughts and carry them to God as their final end.
If the mind is not sufficiently controlled and disciplined at our first engaging in devotion, it contracts certain bad habits of wandering and dissipation. These are difficult to overcome. The mind can draw us, even against our will, to worldly things. I believe one remedy for this is to humbly confess our faults and beg God’s mercy and help.
I do not advise you to use multiplicity of words in prayer. Many words and long discourses are often the occasions of wandering. Hold yourself in prayer before God, like a dumb or paralytic beggar at a rich man’s gate. Let it be your business to keep your mind in the presence of the Lord. If your mind sometimes wanders and withdraws itself from Him, do not become upset. Trouble and disquiet serve rather to distract the mind than to re-collect it. The will must bring it back in tranquillity. If you persevere in this manner, God will have pity on you.
One way to re-collect the mind easily in the time of prayer, and preserve it more in tranquillity, is not to let it wander too far at other times. Keep your mind strictly in the presence of God. Then being accustomed to think of Him often, you will find it easy to keep your mind calm in the time of prayer, or at least to recall it from its wanderings. I have told you already of the advantages we may draw from this practice of the presence of God. Let us set about it seriously and pray for one another.