Shavua Tov. Today’s Parsha has a form of the word שמחה seven times. (As pointed out by Rabbi Sachs in Torah Tidbits)
The holiday of Succot has שמחה mentioned twice. It says, both ושמחת בחגך as well as והיית אך שמח. Both are instructions to be happy during this festival.
The תלמוד ירושלמי expands on this point and says, אין שמחה אלא בשלמים, that real joy comes from the offering of a קרבן שלמים. The תורה תמימה explains this statement by saying that the happiness that comes with the שלמים comes from the fact that the one who offers it, must eat from the meat of the sacrifice. And the way one achieves happiness on the Chag, comes from eating meat.
The obvious question is that we no longer have a קרבן שלמים, so we cannot experience that שמחה. The תורה תמימה claims that this is the reason why wine was added to help reach this level of exhilaration. This is how the expression, אין שמחה אלא בבשר ויין, there is no joy except with wine and meat, evolved.