Yashan
The Pesukim in Parshat Emor [1] introduce us to the prohibition of eating the new grain until the Korban Omer is brought:
ולחם וקלי וכרמל לא תאכלו עד עצם היום הזה עד הביאכם את קרבן אלהיכם חקת עולם לדרתיכם בכל משבתיכם:
The Sefer HaChinuch [2] explains to us that the underlying message we can derive from the mitzvah is that since grain is the most essential food of substance that Hashem gives us to live and in order to recognize Him we refrain from enjoying it until a Korban is brought before Hashem similar to a Bracha prior to indulging in food. [It should be obvious that this is only a nice idea one can learn from the Torah but certainly not a halachically binding reason.]
There’s a major discussion about the applications of this prohibition especially nowadays and outside Israel. Because this is an issue that has existed for many centuries there’s a plethora written on the topic and hopefully B”H this article will summarize the main points that are relevant for the contemporary issue.