הלכה על ברכות 69:21

It is from the roots of the commandment [that it is] since the main nourishment of the creatures is from grains. And therefore it is fitting to offer from them a sacrifice to God who gave them, before the creatures benefit from them. And [it is] similar to that which they, may their memory be blessed, said about [something] resembling this (Berakhot 35a), "Anyone who benefits from this world without a blessing has misappropriated." And all of this is to prepare ourselves that we should be fitting to receive from His goodness - and as I wrote in this book many times. And at the time of the [Temple], on the sixteenth of Nissan, we would offer the sacrifice of the omer from the new grain barley grain, since it is the grain that comes out first [before] the wheat. And it permits [us to benefit from] all of the grains.