Concentration bestows serenity or calmness of mind, inner spiritual strength, patience, great capacity to turn out tremendous work, alacrity, acumen, agility, beautiful complexion, sweet voice, brilliant eyes, powerful voice and speech, power to influence others and attract people, cheerfulness, joy, bliss of soul, supreme peace. It removes restlessness, agitation of mind, laziness. It makes you fearless and unattached. It helps you to attain God- realisation. The more is the mind fixed on God the more is the strength you will acquire.
More concentration means more energy.
Concentration opens the inner chambers of love or the realm of eternity. Concentration is a source of spiritual strength. Be slow and steady in concentration. By practice of concentration, you will become superhuman. Those who practise concentration off and on will have a steady mind only occasionally.