Rosh Hashanah, Chapter 3, Mishnah 8. The previous Mishnah dealt with cases in which a person's intent plays a decisive role in the fulfillment of a mitzvah. Our Mishnah too addresses the significance of intent, even though it does not deal directly with the fulfillment of a mitzvah.
The War Against Amalek and Moshe's Raised Hands:
The Mishnah describes Amalek's war against Israel in the wilderness: Moshe went up to pray, and as long as he raised his hands Israel would prevail, and when he lowered them they would suffer defeat. In the words of the verse the Mishnah cites: "Vehayah ka'asher yarim Moshe yado vegavar Yisrael" - "And it was, when Moshe raised his hand, Israel prevailed," and so on.
On this the Mishnah asks a piercing question: "Vechi yadav shel Moshe osos milchamah o shovros milchamah?" - do Moshe's hands win the war or cause the defeat? Does the matter really depend on his hands?
Rather, the verse comes to teach you: as long as Israel looked upward and subjected their hearts to their Father in Heaven, they were victorious and prevailed; and if not, they would fall. As long as they lifted their eyes to Heaven, placed their trust in Hashem and prayed to Him, they had the upper hand; and when they did not do so, they fell in battle. Moshe's raised hands were nothing more than a symbol of this.
A Similar Case - the Copper Serpent:
The Mishnah brings another incident from the wilderness: the Children of Israel complained about the manna, and the Holy One, Blessed is He, sent venomous fiery serpents among them that bit them. When Moshe prayed, the Holy One, Blessed is He, commanded him to make a serpent of copper and place it upon a pole, and whoever gazed at it would be healed, as it says: "Aseh lecha saraf vesim oso al nes, vehayah kol hanashuch vera'ah oso vachai" - "Make yourself a fiery serpent and place it on a pole, and it shall be that anyone who was bitten will look at it and live."
Again the Mishnah asks: "Vechi nachash memis o nachash mechayeh?" - does the copper serpent that Moshe made kill a person, or does it give him life?
Rather, here too the matter is symbolic: when Israel looked upward and subjected their hearts to their Father in Heaven, they were healed; and if not, they would waste away and sink.
Who Can Fulfill the Obligation on Behalf of Others:
The Mishnah concludes with a halachic element, with the question of who is fit to help another fulfill his obligation in a mitzvah: "Cheresh, shoteh vekatan ein motzi'in es harabim yedei chovasan" - a deaf-mute, a mentally incompetent person and a minor cannot fulfill the obligation on behalf of the many:
Cheresh - one who is deaf and mute.
Shoteh - one who is not of sound mind.
Katan - one who has not yet reached the age of bar mitzvah.
These three cannot fulfill the obligation of others in the mitzvah of shofar, nor in the other mitzvos, because they themselves are not obligated in mitzvos. In order to fulfill another's obligation, the one doing so must himself be obligated in that mitzvah and capable of performing it.
And so the Mishnah sums up: "Zeh haklal: kol she'eino mechuyav badavar - eino motzi es harabim yedei chovasan" - this is the rule: anyone who is not obligated in a matter cannot fulfill the obligation on behalf of the many. One who is not obligated in a mitzvah has no power to fulfill others' obligation in it.
In summary: In this Mishnah we learned from two events that took place in the wilderness - Moshe's raised hands during the war against Amalek, and the copper serpent that healed those who had been bitten - that the power lies neither in the hands nor in the serpent, but in subjecting the heart to their Father in Heaven and in looking upward. At the close of the Mishnah we examined the halachic rule that a cheresh, a shoteh and a katan cannot fulfill the obligation on behalf of the many, because they are not obligated in the matter - and anyone who is not obligated in a matter cannot fulfill the obligation on behalf of the many.