The general expression used throughout the generations to wish each other well on holidays is Chag Sameach – Happy Holiday. However, just as each holiday has its own particular meaning and content, it also has its own particular greeting. The greeting for Shavuot is le Kabalat ha Torah beSimcha u bePnimiut – [may this holiday be for] the joyful and internalized reception of the Torah.
Let's briefly analyze the liturgy of the greeting. The first matter is specific to the festival of Shavuot, which is, among other events, zman matan Torah – the time of the Giving of the Torah. We wish that we may truly receive the Torah. Because this is an ongoing event, as indicated by the fact that when we recite the morning blessing for the Torah or when we make an aliyah to the Torah, we say, "Blessed are You, God, who gives the Torah." That is to say, constantly, moment by moment, God gives us the Torah (and it is not an event that happened once and then passed).
The next concept is Simcha – Joy. In Jewish law, Simcha is spoken of during the holidays, expressed in the eating of meat and drinking wine (in the Kiddush – sanctification). It could be added that the idea here is that one should not view the Torah and its mitzvot as a heavy burden, but rather study the Torah and observe the mitzvot with Simcha – with the joy of knowing that one is serving the King of all Kings, the Holy One, blessed be He, and at the same time, improving oneself and the world around one.
And finally, internally. The Torah must penetrate deeply into a person's life, to the point where one becomes one with the Torah; that is, all aspects of life become holy (not only those that God defines as holy, the Mitzvot) and channels through which God reveals Himself on Earth.
The way to achieve personal fulfillment of these expressions is through the study of the Torah, which gives us the possibility of feeling joy in the connection with God and gives us the strength to imbue our lives with holiness.
May we receive the Torah this Shavuot with joy and internalize it.