In this week's Parsha, we read of the ברית established between Hashem and Bnai Yisrael at Har Sinai. Although the Aseres HaDibros themselves are recorded in last weeks Parsha, the details of the Bris at Har Sinai are found at the end of our Parsha (פרק כ"ד). One of the important elements of this ברית was the sprinkling of the blood from the Korbanos (burnt offerings and peace offerings) brought by the people. The Pesukim state that Moshe took half of this blood and sprinkled it on the altar he had built, and the other half he sprinkled onto the people after having read them the terms of the ברית (שם פסוקים ו'-ח').
Rabbeinu Chananel understands that this ברית contained a great deal of symbolism. Blood represents life, and thus the prominent role played by the blood in this ברית signifies the idea that if Bnai Yisrael fulfill the Mitzvos of the Torah, their lives will be good, while if they don't, their lives -their blood- will be forfeited. It seems obvious that the blood which was sprinkled onto the people was really sprinkled onto their clothing; they therefore had on their bodies a reminder of this ברית with Hashem. Rabbeinu Chananel in fact understands that the special ornaments which Bnai Yisrael had to remove after sinning with the Golden Calf, as described later in the Torah (שמות ל"ג:ה-ו'), were actually these clothes which had the sprinkled blood upon them. After they worshipped the Golden Calf, thereby ignoring the ברית with Hashem, He commanded them to remove this special clothing until they were forgiven. Today, of course, we do not have that kind of visual reminder of the ברית with Hashem; we thus must find some other way of reminding ourselves of it constantly.