According to the Talmud, a person “should always complete his Torah portion with the community and study the Torah twice and the translation once” (Berachot 8a).
In the first century, Onkelos, the most famous convert of the era, penned the official Aramaic translation to which the Talmud refers. Even nowadays his masterpiece is still printed in almost every Chumash.
The Shulchan Aruch suggests reading Rashi’s interpretation instead of Onkelos’s, as almost no Jews spoke Aramaic by the Middle Ages.
The remarkable principle behind this rabbinic enactment is the expectation that every Jew have a thorough grasp of the Torah and that study does not come to an end with adulthood. The idea is that one should study the weekly Torah portion; read it twice in the original and once in translation. With everyone’s learning in sync, we have greater opportunity to learn from each other and grow together.