It's not an obligation upon you to finish the work. Talking about Torah study, a person could get very intimidated. We have the whole entire Torah. We have so many sefarim (books) out there. You look at a bookshelf, and a person could say, “I'm not going to ever have the ability to finish this in my entire life.” So the Mishnah is comforting that person, saying it's not about the destination of finishing; it's about you. It's about your hard work that you put in. If you put a lot of effort in, it's not about finishing the job; it's just doing as much as you can. You're never going to be the master of all of Torah, but it doesn't mean that a person should give up and say, “I'm not going to get it all done; I'm not going to try it all.” But no, it's okay not to get it all done, but you have to work very hard.
It's not about finishing, but it's about the effort that you put in. But at the same time, but you're not free to be lazy and to nullify yourself from Torah study. We're not expected to master the entire Torah, and a person may think, “You know what? Okay, if I'm not supposed to master it, I'll just put a little bit of effort in. It's a little bit of work; I'll know a little bit of Torah, and that'll be it.” What we're saying here is, no: you're not free men who could do whatever you want, but rather, we're servants of HaKadosh Baruch Hu, and HaKadosh Baruch Hu wants us to work hard in Torah, yomam valayla, day and night, and therefore, we're not free men to just decide what we want to do. We have to pursue greatness, even though mastery of the entire Torah may not necessarily be there.
If you learn a lot of Torah, they're going to give us a lot of reward. There's a tremendous incentive for a person to work very hard on Torah. The more Torah somebody learns, the more reward he's going to receive. Even if a person mastered all of Torah, all of Shas, all of the Poskim (halachic decisors), all of the Tanakh, all of the Ba'alei Musar (masters of ethical teachings), all of Chassidut (Hasidic teachings), he studied everything, and he knows it all, cold. There's still reward? By Chassidut. It never ends. It's a continuous cycle through Torah learning until a person knows everything, and then beyond that, through his Chazarah, through his reviews.
And your employer, Hashem, could be relied upon to pay you the wages of your work. Hashem, who told us that we have to study Torah, told us as well that He's going to reward us in Olam HaZeh (in this world) and in Olam HaBa (world to come) for following the commandments and for learning Torah. You have to know: even though we said that a person receives reward in Olam HaZeh, in this world, the main reward is in Olam HaBa, in the future, when a person goes to Olam HaBa. The majority of the reward can't be recognized by somebody while he's in Olam HaZeh, but the main reward is put away in a spiritual way for the Tzadikim (righteous people) in the world to come.