know what you chant...

ऋचेऽक्षरे परमे व्योमन् यस्मिन्देवा अधिविश्वे निषेदुः।

यस्तन्न वेद किमृचा य इत्तद्विदुस्त इमे समसते॥ 

ऋग्वेदम् १-१६४-३९

ṛce'kṣare parame vyoman yasmindevā adhiviśve niṣeduḥ|

yastanna veda kimṛcā ya ittadvidusta ime samasate|| 

ṛgvedam 1-164-39

स्थाणुरयं भारहारः किलाभूदधीत्य वेदं न विजानाति योऽर्थं।

योऽर्थज्ञ इत्सकलं भद्रमश्नुते नाकमेति ज्ञानविधूतपाप्मा॥ 

यास्कप्रणीते निरुक्ते १-१८-२०

sthāṇurayaṁ bhārahāraḥ kilābhūdadhītya vedaṁ na vijānāti yo'rthaṁ|

yo'rthajña itsakalaṁ bhadramaśnute nākameti jñānavidhūtapāpmā|| 

yāskapraṇīte nirukte 1-18-20

The Vedas and the commentators on them have always held the view that mere parrot-like recital of the mantras or hymns without having any clue about their meaning and context are of no uses..

Rigvedam Says.. 

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All the divine beings are residing in the hymns of veda which are eternal, vast in meaning and of great merit .. and if a person recites those hymns without knowing the presence of the divine and the meaning of the hymns is wasting his time.

And the one who knows or is taught about such meaning would derive benefits and would attain the presence of such divine beings..

Sage Yaska in his Niruktham says

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A person who memorizes the hymns of the vedas without knowing their meaning is just like a solid granite structure erected on the roadside where wayfarers could place their burdens and take rest..

A person who understands the meaning of the Vedic hymns he has learned attains all comforts and merits. He attains enlightenment.. His sins are washed away. And he attains the world of eternal happiness.