Mind is a bundle of habits. Bad habits and prejudices, hidden in one's nature, will be brought to the surface of the mind when the opportunity comes. If you change the habits you can also change your character. You sow a habit and reap a character. You sow a character and reap a destiny.
Habits originate in the conscious mind but when they become established, by constant repetition, they sink into the unconscious mind and become our 'second nature'. Habit can however be changed by a new, healthy, agreeable habit, of a stronger nature. At present you are thinking, "I am the body". Think, "I am Brahman". In the course of time you will be established in Brahmic consciousness.
Do not be a slave to one idea. Whenever you get new, healthy ideas, the old ones must be given up. In the mind there is an internal fight ever going on between 'nature' and 'will', between the old, worldly habits and the new, spiritual habits.
In the case of aspirants, the fight is between the old samskaras of the sensual world and new, spiritual samskaras. It is a fight between the good impressions of the past and bad impressions of the past. It is a fight between viveka (wisdom) and instinctive mind and indriyas (senses).
Eventually will, which is pure, strong and irresistible, is bound to succeed. There is no doubt about this. As your reason grows and you become wiser and wiser - by study, by contact with the wise and by meditation - your mind must be well prepared to take up new, healthy, rational ideas and eschew the old, morbid ones.
Mind is your tool. When emotions arise, separate them, study them, analyse them - but do not identify yourself with them. Master your impulses, emotions and moods. Rise from the position of slave to that of a spiritual king.
Just as the repetition of a thought or action leads to perfection, so also does the recurrence of the same process, or the same idea, lead to the perfection of abstraction, concentration and meditation.
Give your full mind to God. Only then will you have realisation. Even if one ray of the mind runs outside, it is impossible to attain God-consciousness. You cannot enjoy peace of mind, you cannot practise meditation, if there is tossing of the mind. Destroy mundane desires through dispassion and surrender to the Lord.