We try to engage all the members of the Krsna consciousness movement in the service of the holy name. Since the holy name and Krsna are nondifferent, the members of the Krsna consciousness movement not only chant the holy name of the Lord offenselessly, but also do not allow their tongues to eat anything that is not first offered to the Supreme Personality of Godhead.
The Supreme Lord declares:
patram puspam phalam toyam yo me bhaktya prayacchati
tad aham bhakty-upahrtam asnami prayatatmanah
“If one offers Me with love and devotion a leaf, a flower, a fruit or water, I will accept it.” (Bg. 9.26) Therefore the International Society for Krishna Consciousness has many temples all over the world, and in each and every temple the Lord is offered these foods. On the basis of His demands, the devotees chant the holy name of the Lord offenselessly and never eat anything that is not first offered to the Lord. The functions of the tongue in devotional service are to chant the Hare Krsna maha-mantra and eat prasadam that is offered to the Lord.
Srila Prabhupada, CC Adi 8.16, ppt.