When you come into the land which the L!RD your G!D gives you as an inheritance, and you possess it and settle in it, then you shall take the first of all the fruit of the earth which you bring forth from your land that the L!RD your G!d is giving you, and put them in a basket and take them to the place that the L!RD your G!d chooses for His Name to dwell. Deuteronomy 26:1-2
My grandfather and teacher [Yitzhak Meir, the first rebbe of Ger, the Chiddushei HaRIM] said that prayer is in place of the firstfruits, for we offer them at the first of the day, when we have just awoken from our sleep and immediately we remember G!d, and rejoice in the return of our souls to this world, so that we may serve G!d all the day.
If you obey the L!RD your G!d and listen to His commandments…then all these blessings will come upon you and cleave to you. Deuteronomy 28:1-2. (1)
The essence of fulfilling a mitzvah is to do it with joy and love, and according to how you long all the day to do mitzvot, so will you be enabled to truly do them. This is why we say a blessing before we perform a mitzvah, to show how beloved it is to us. In such preparation for the mitzvah there is blessing, an enlightenment that will stay with us throughout the day. This is the meaning of what Rabbi Shimon ben Gamliel said: “Any mitzvah that the Children of Israel received upon themselves with joy, they continue to do with joy” (2).
1) It’s not clear which Torah verse this teaching connects to, so I supplied the one that made most sense to me. 2) Shabbat 130a