Concentration means inner vigilance and alertness. There are thieves all around us and within us. Fear, doubt, worry and anxiety are inner thieves that are trying to steal our inner poise and peace of mind. When we learn how to concentrate, it is very difficult for these forces to enter into us. If doubt enters into our mind, the power of concentration will tear doubt to pieces. If fear enters into our mind, the power of concentration will chase away our fear. Right now we are victims to unlit, obscure, destructive thoughts, but a day will come when, on the strength of our concentration, disturbing thoughts will lie afraid of us.
Concentration is the mind's dynamic will that operates in us for our acceptance of light and rejection of darkness. It is like a divine warrior in us. What concentration can do in our life of aspiration is unimaginable. It can easily separate Heaven from hell, so that we can live in the constant delight of Heaven and not in the perpetual worries, anxieties and tortures of hell while we are here on earth.
Concentration is the surest way to reach our goal, whether the goal is God-realisation or merely the fulfilment of human desires. A real aspirant sooner or later acquires the power of concentration either through the Grace of God, through constant practice or through his own aspiration.