According to Judaism, what is man's duty in this world, and what should man's goal in life be?
Is our goal to fulfill G0d's commandments, which will earn us a place in Olam Haba, or is our goal merely to serve Hashem, altruistically, without any thought about possible reward?
Or perhaps, is our duty and goal something totally different?
Man's duty and goal can be looked at from two vantage points: 1). From Hashem's view 2). From our own.
According to the Ramchal (Derech Hashem, Daat Tvunos, etc...) Hashem wanted to give and so he decided to create something to receive ultimate goodness. However, for a number of reasons (see there) he wanted man to have free choice and be able to do positive things with his free choice.
By being the "cause" of good we accomplish what Hashem wanted us to do. This I believe is our "duty" as I see, this is want Hashem wants from us. Our goal is to connect to Hashem. As the Ramchal mentions (Daas Tvunos Chelek 4) by perfecting ourselves Hashem can connect more directly with us and have "הארת פנים" which I understand is connected if not synonymous with the "ultimate good" - ie: being connected to Hashem.
In reality these are one in the same, our perfection (ie: the good we cause) enables the connection and our destructive acts block or turn Hashem away from us. See Ramchal there.
1). Hashem wants us to "earn"/"deserve" Olam Haba (you can't truly earn it even if you did every Mitzvah and no aveira, what does Hashem owe us? I recall a Ramban to this effect on Chumash, but I think logical).
2). We want to connect to Hashem... the "reward" is incidental imo. (See Michtav Meliyahu (חלק ב׳) on Elul where there is practical advice imo on how to accomplish this (הצנע לכת) - his goal there is to remove haughtiness, but I think it can apply here too).
Torah and Mitzvot.
The world exists only for the sake of Torah (Pesachim 68b)
Torah and Mitzva are practically synonymous:
And I will give you the tablets of stone, the Torah, and the Mitzvah (Shemot 24:12)
The Torah and Mitzvot are Hashem's Wisdom and Will absolutely (Tanya Ch. 34). By performing them, we are fulling our reason for being created; our mission and purpose. This is to serve Hashem, and this is considered a service because we are performing His Will, i.e. giving Him what He wants.
Ideally yes, they should be done altruistically, without thought of reward.
Antigonus a man of Socho... used to say: do not be like servants who serve the master in the expectation of receiving a reward, but be like servants who serve the master without the expectation of receiving a reward
This takes explanation and as Micha Berger rightly pointed out, it takes a book (at least). However, as a summary and introduction to encourage the reader to take on further study:
It says in Derech Hashem that Hashem created the world in order to give goodness from His goodness to another (1:2:1). He then proceeds to explain that our duty is to emulate Him, and this is how we receive that good.
So what we know so far is that the best good is Hashem, and what's good about Him is that His desire is to give to another. Therefore conclude that the best good of all is giving to others (serving others).
He gave us a good mashal in Shir Hashirim:
I am for my beloved, my beloved is for me (6:3)
There are quite a few ways a relationship can work. Both parties can be selfish but complement each other and therefore exist in a functional relationship with some goodness. This is not Godly though, and therefore not the best good.
The best good is when both parties are into each other more than they are into themselves. The only way to make sense of this, is following the line of the Rambam on the Mishna in Avot:
And this pious one said that you should not serve God, may He be blessed, in order that He will do good to you and benefit you with kindness and that you should hope for the benefit and serve Him for its sake. Indeed, serve Him like servants that are not hoping for endowment or the giving of kindness. He meant with this that they should serve Him from love, as we said in Chapter Ten of Sanhedrin.
and what Ramchal states clearly in Mesilat Yisharim Chapter 18:
"Fortunate is the man whose toil is in the Torah and gives gratification to his Maker"... he who truly loves the Creator, blessed be He, will not strive and intend to discharge himself with the known obligations binding on every Jew. Rather, what will happen to him is the same as that of a son who loves his father. Even if his father reveals a slight indication of something he desires, already the son will strive greatly, to the best of his ability, to fulfill this thing or service.
Conclude from all this that the greatest good is serving others, one's beloveds.
Taste, and see that Hashem is good (Tehillim 34:8)
By default, our entire orientation in life is to gain pleasure by fulfilling our own desires and wants. During that time, the idea of serving others being pleasurable sounds far fetched, and at best a nice little idea that is probably true to some extent. The truth is, it takes wisdom (via Torah learning) and experience (i.e. taste it, via performing Mitzvot, especially the Mitzva to get married) for one to see the truth of it.
A truly holy and devoted husband will tell you, hands down, no pleasure or wonder of the universe could possibly compare to the delight he takes in bringing his wife a coffee in the morning. Not because he will get a reward out of it, but actually serving her, fulfilling her needs great and small, is its own reward. He is for his beloved, not himself, his own needs and desires pale in comparison to hers - he feels the tug of her need as a true delightful privilege for him to be able to serve - and he has been blessed to experience a taste of true goodness and Godly delight.
So now we can understand our Mishna. Is there reward in serving Hashem and each other? Yes, the best reward imaginable. Should we be doing it for that reward? No, this ruins it. It is no longer a true service, it is simply a self service, and adds a bitter taste to what should be only sweet - fulfilling the needs and desires of someone else, because one is completely and utterly devoted, one, with them.
שְׁמַע יִשְׂרָאֵל ה' אֱלֹקֵינוּ ה' אֶחָֽד
As we stated above, the Torah and Mitzvot are Hashem's absolute Will. Therefore by performing them, we are truly serving Him. In-so-doing, we are emulating Him and becoming One with Him, and we will receive Him in Olam Haba (as our "reward", see Derech Hashem 1:2 onwards). Another way to see it, don't read Hashem gave us the purpose of receiving the best good. Hashem's purpose is to give the best good. It's His purpose, not ours. Ours, as stated above, is Torah and Mitzvot and in-so-doing emulate Hashem by giving from our goodness to others.
The Lubavitcher Rebbe clarifies for us a couple of points:
The astute reader will read between the lines and see what the greatest goodness of all is - having each other, not the things about each other. "I don't want Your Olam Haba, all I want is You" - Alter Rebbe. It's enough to, so to speak, satisfy God, and if we follow His guidance (Torah), we will taste it for ourselves, and by keeping the Mitzvot, we will bring about this great Oneness He is after, for His sake, and for the sake of everyone. We might also enjoy it too, but let's not focus on that :)
והיה ה' למלך על־כל־הארץ ביום ההוא יהיה ה' אחד ושמו אחד (Zacharia 14:9)
May this great day arrive without delay.
Rabbi Moshe Chaim Luzzato (known as the Ramchal), in his work "Mesilas Yesharim" (beginning of Chapter 1) expresses it as such:
יסוד החסידות ושרש העבודה התמימה הוא שיתברר ויתאמת אצל האדם מה חובתו בעולמו ולמה צריך שישים מבטו ומגמתו בכל אשר הוא עמל כל ימי חייו.
The foundation of piety and the root of perfect service [of G-d] is for a man to clarify and come to realize as truth what is his obligation in his world and to what he needs to direct his gaze and his aspiration in all that he toils all the days of his life.
והנה מה שהורונו חכמינו זכרונם לברכה הוא, שהאדם לא נברא אלא להתענג על ה' ולהנות מזיו שכינתו שזהו התענוג האמיתי והעידון הגדול מכל העידונים שיכולים להמצא. ומקום העידון הזה באמת הוא העולם הבא, כי הוא הנברא בהכנה המצטרכת לדבר הזה.
Behold, what our sages, of blessed memory, have taught us is that man was created solely to delight in G-d and to derive pleasure in the radiance of the Shechina (divine presence). For this is the true delight and the greatest pleasure that can possibly exist. The place of this pleasure is, in truth, in Olam Haba (the World to Come). For it was created expressly for this purpose.
אך הדרך כדי להגיע אל מחוז חפצנו זה, הוא זה העולם. והוא מה שאמרו זכרונם לברכה (אבות ד): העולם הזה דומה לפרוזדור בפני העולם הבא.
But the path to arrive at the desired haven of ours, is this world. This is what our sages of blessed memory said: "this world is like a corridor before the World to Come" (Avot 4:16).
והאמצעים המגיעים את האדם לתכלית הזה, הם המצוות אשר צונו עליהן האל יתברך שמו. ומקום עשיית המצוות הוא רק העולם הזה. על כן הושם האדם בזה העולם בתחלה כדי שעל ידי האמצעים האלה המזדמנים לו כאן יוכל להגיע אל המקום אשר הוכן לו, שהוא העולם הבא, לרוות שם בטוב אשר קנה לו על ידי אמצעים אלה. והוא מה שאמרו, זכרונם לברכה (עירובין כב א): היום לעשותם ומחר לקבל שכרם.
The means that lead a person to this goal, are the commandments which the blessed G-d commanded to us. The place of the performance of these commandments is only in this world. Therefore, man was first placed in this world so that through these means prepared for him here, he will be able to reach the place prepared for him, namely, the World to Come, there to be sated with the good which he acquired through these means. This is what our sages of blessed memory said "today to do them, and tomorrow to receive their reward" (Eruvin 22:1).
