(1) Meditation helps to calm the mind and get it better organised.

(2) It strengthens our will power and enables us to face all problems and hardships with confidence.

(3) It guides us think positively

(4) It improves our efficiency in work by helping us to concentrate better and by sharpening our mental faculties

(5) It frees us from worries, restlessness, fatigue, stress and blood-pressure.

(6) It increases our mental health and therefore bears a positive effect to a large extent on our physical health and thereby an awakening in all our day today activities.

(7) It helps cleanse our mind of defilements (Kilesa)

(8) It creates in us virtuous qualities like kindness, inner peace, humbleness (as opposed to arrogance), a realistic attitude towards life and it prevents us from being influenced by such elements as passion, selfishness, hatred, jealousy, malice, taking revenge or greed.

(9) An untrained person is often dominated by delusion or ignorance (Avijja) and his own pre-conceptions which prevent him from having proper insight into reality. Meditation helps to remove such unwholesome effects in a person.

source : Thebuddhism.net