Srimadbhagavadgita -यथा दीपो निवातस्थो नेगंतेसोपमा स्मृता- AllinharidwarAllinharidwar

यथा दीपो निवातस्थो नेगंतेसोपमा स्मृता। योगिनो यतचितस्य युञ्जतो योगमात्मन:। Srimadbhagavadgita (chapter 6, 19th shloka)
Meaning:- As a light does not Flicker in a windless place, such is supposed to be the image of the well disciplined mind of the yogi meditating on God.
Explanation: Lord Krishna is teaching Arjun that a Yogi’s mind must be standing still to practice meditation on God just like a lamp in a windless place where the flame does not flicker and enlightens it(the place).
A well disciplined mind does not get attacked to any object and concentrates on the objective only. People come holy places and pretend that they have renounced everything and just practicing sadhna of the almighty God but their mind does not stop to follow temptations. Consequently they do not attain the Moksha(the ultimate goal of life). Therefore a Yogi has to close the door of his/her mind so that no unwanted thought can distract it from the meditation.