Though it is important to know the meaning of the Vedic Mantras, it is not mandatory for performance of the Vedic karmas. As many cannot understand and comprehend the inherent meaning of the Vedas, it is enough if they do the Vedic rituals with full faith.
arthajnAnam na karmAngam !
na ca avidusha: karmANi anadhikArah, aushastye kANde avidushAmapi Artvijya darSanAt !
tasmAt avidushopi karmaNI adhikArah !
Thus a dvija who is not aware of the meaning of the Vedas is fully qualified for performance of Vedic rituals. What is more important is SraddhA (utmost faith) in Vedic scriptures.
जय जय श्रीराधे