Concentration or dhāraṇā is the initial step of deep concentrative meditation where the object being focused upon is held in the mind without consciousness wavering from it. The fixing of the mind can be on something external or internal like a sacred picture or on any other object or point, internally it can be fixed on any chakra or any part of the body or on any abstract idea.
The practise of concentration gives a very good health and very clear mental vision as concentration develops penetrative insight. Subtle esoteric meanings will flash in the field of mental consciousness, it will be possible to understand the inner depths of philosophical significance in the traditional texts for example.
Those who practise concentration evolve quickly, they can do any work with greater efficiency. Concentration purifies and calms the surging emotions, strengthens the current of thought and clarifies the ideas.
Concentration keeps a man in his material progress also, what was cloudy and hazy before, becomes clearer and definite; what was difficult before becomes easy and what was complex, bewildering and confusing before, comes easily within the mental grasp. Nothing is impossible for one who practises regular concentration.