Swami Yatiswarananda: “If you attempt meditation without having attained purity of mind, you are likely to concentrate more on the impurities of the mind than on God…When you sit alone and try to quieten the mind, forbidden impure thoughts begin to rise in your mind and create confusion. These may even overpower you…Without attaining a certain amount of sublimation and purification of the feelings and desires, concentration becomes very dangerous in the case of persons who have not prepared themselves properly for the higher life. It may lead to very bad effects.
“In a way, we all make the mind concentrated, but then we do not know how to manipulate. This concentrated mind will run after sensual enjoyments and all kinds of worldy distractions and objects with a greater intensity for having become concentrated. So, if we do not know how to handle the mind in the right way, it may lead us astray. It is far better not to have concentration if one does not attain sublimation and purification at the same time. Therefore, the necessity of purity, non-injury, truthfulness, continence, etc., in thought, word and deed, has to be stressed very much.
“Without sublimation of all our desires and feelings, we cannot progress in the spiritual path. It is only after we have followed a strict code of ethics and morals that we should attempt concentration and meditation. The concentrated mind, if it is not purified, becomes a veritable demon and creates no end of troubvles for the spiritual aspirant.”
(pgs. 327-328, Meditation & Spiritual Life)