You tell me nothing new; you are not the only one who is troubled with wandering thoughts. Our mind is extremely roving; but as the will is mistress of all our faculties, she must recall them, and carry them to God as their last end.
       When the mind, for want of being sufficiently reduced by recollec-tion at our first engaging in devotion, has contracted certain bad habits of wandering and dissipation, they are difficult to overcome, and commonly draw us, even against our wills, to the things of the earth.
       I believe one remedy for this is to confess our faults and to humble ourselves before God. I do not advise you to use multiplicity of words in prayer, many words and long discourses being 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 it sometimes wanders and withdraws itself from Him, do not much disquiet yourself for that: trouble and disquiet serve rather to distract the mind than to recollect it; the will must bring it back in tranquility. If you persevere in this manner, God will have pity on you.
       One way to recollect the mind easily in the time of prayer, and preserve it more in tranquility, is not to let it wander too far at other times.  You should keep it strictly in the presence of God; and 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.
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Brother Lawrence, The Practice of the Presence of God