The Literal Commandment
Until this same day, until you have brought in the offering of your God, you shall eat neither bread nor roasted grain nor new growth. It is to be a perpetual statute throughout your generations in all your dwelling places." (Leviticus 23:14)
The literal commandment is that we are not to eat new growth (ripened grain) from the new grain until "the offering" (first-fruits offering) has been brought in.