We are up to Mishnah 23 of chapter 5 (in some editions it is numbered as Mishnah 25) - the last Mishnah of the chapter, and in fact the last one in the entire tractate. The next chapter is not made up of actual Mishnayos, but of Beraisos. This Mishnah is short, sharp and especially important.
The author of this Mishnah is Ben Hei Hei, who was apparently also a convert. "Ben Hei Hei" is not his real name but a sort of nickname, perhaps meant to conceal his identity. The letter hei in his name is the letter that Avraham Avinu and Sarai Imenu added to their names, and it refers and alludes to the Name of the Holy One, blessed is He.
And this is what he said, in Aramaic: "L'fum tza'ara agra" - according to the tza'ara, which means pain and suffering in the plain sense, so is the agra, the reward and the recompense.
Reward according to the effort:
The basic idea here is very simple, but it is central to all of Jewish thought: the heavenly recompense, the reward a person receives in the World to Come, is a function of how much effort he invested. The intentions, the planning, the trouble, the concentration, the exertion, the hard work, the money and resources laid out - everything a person invests in his service:
In Torah study.
In fulfilling the mitzvos.
In changing bad character traits into good ones and refining his middos.
In helping others.
All of these are good deeds, reward and merit, but the measure of reward a person receives for them is determined by the amount of effort he invested in them, in all the aspects described.
There are no shortcuts:
There are no tricks and there is no magic. A person's purpose here in life is to build a relationship with the Holy One, blessed is He, and the way to do that is through Torah and mitzvos. In the end it all comes down to that relationship, and a relationship is a function of choice. A person is by his very essence a chooser; free will is what defines who we are. And what drives it is not merely the idea in one's head - "I would like to do something, or I would not like to" - but rather the action a person takes in order to make it happen.
Therefore, when something comes to a person easily, there is nothing wrong with that and he indeed does it, but there is no real building of a relationship with the Holy One, blessed is He, in it. He is simply pre-programmed that way by his inclination, his personality and his genetics. But when he overcomes his nature, or takes the good inclination and runs forward with it and invests more in doing the right thing - in time, in effort, in resources, in planning, in toil, in hard work, in money, in thought and in concentration, and also in patience, persistence and determination - that is his investment in the relationship with the Holy One, blessed is He, and that is what will determine the measure of his reward in the World to Come.
Every person can be a tzaddik like Moshe Rabbeinu:
This is a basic yet central idea, and with it the tractate concludes as it was originally understood. A person should not be saddened that he has not accomplished as much in Torah and mitzvos as others have; it all depends on the effort he invests. A person can be a tzaddik like Moshe Rabbeinu - every single one of us. We cannot be a prophet like Moshe, we will not be as wise as he was, and we will not have the resources and the strength he was born with. But in terms of the potential of each one of us to use his free will, to exert himself in serving Hashem and to cultivate the relationship with the Creator to the fullest of his abilities - everyone can do that. And one who does so becomes a tzaddik like Moshe Rabbeinu, and is worthy of a reward like the very greatest of the great.
And so, with God's help, as we conclude Maseches Avos, it is fitting that we reflect on the advice Chazal have given us throughout the tractate and do our best to put it into practice: to truly exert ourselves and become the very best that we are capable of being.