Why are we obligated to learn Torah she’b’al Peh with meforshim (including Rash"i)? toda Shalom Tzvi-Gad

Shalom, The first reason we learn the Oral Torah (Mishna and Gemara) with the meforshim (early and later commentators) is so we can understand what we are learning. I doubt that there is anyone today skilled enough to open up a page of Talmud, or even many of the Mishnaiot, and understand what is written there without some form of commentary. The next reason is because those commentaries are Torah in and of themselves. Learning Rashi or Tosafot on the Talmud is also part of the mitzvah of learning Torah. Even if someone could grasp the text without their comments (unlikely - see above), learning them expands the depth and scope of the Torah being learnt. Also, we learn the commentators because they make up the chain of tradition that is part of the process needed to reach the practical application of the law. One may certainly come up with new and novel interpretations of the Oral Torah, but in the task of reaching the practical application of the law (halacha) one must take the earlier interpretations into account. If in the process of learning one wishes to explain the text in a way that is not in line with the earlier commentators, (with no attempt to reach or codify halacha) one may do so on two conditions - firstly, that ones efforts are in order to increase their service of Hashem, and not to mock or belittle the Torah. And secondly, that what one says is not contradicted by other explicit sources, or the general spirit Judaism. Even so, I am sure that one's success in such an effort will be greater according to the amount of Torah one has first learnt with the standard commentators who have shone their light on the texts throughout the generations.