From where/Why do you get more reward for doing a obligated mitzvah than a non obligated mitzvah?

Question

Ive heard (not sure where)that you get more reward for doing a obligated mitzvah than a non obligated mitzvah. Where is this brought down, and whats the reason for this?

Answer 1

The source that someone obligated in a mitzvah receives more reward than someone not obligated is a statement of R. Chanina which appears several times in the Talmud. The first appearance is Kiddushin 31a.

וא"ר חנינא ומה מי שאינו מצווה ועושה כך מצווה ועושה עאכו"כ דאר"ח גדול מצווה ועושה ממי שאינו מצווה ועושה אמר רב יוסף מריש ה"א מאן דהוה אמר לי הלכה כר"י דאמר סומא פטור מן המצות עבידנא יומא טבא לרבנן דהא לא מיפקידנא והא עבידנא השתא דשמעיתא להא דא"ר חנינא גדול מצווה ועושה יותר ממי שאינו מצווה ועושה אדרבה מאן דאמר לי דאין הלכה כרבי יהודה עבידנא יומא טבא לרבנן

Now, R. Hanina observed thereon, If one who is not commanded [to honour his parents], yet does so, is thus [rewarded], how much more so one who is commanded and does so! For R. Hanina said: He who is commanded and fulfils [the command], is greater than he who fulfils it though not commanded. R. Joseph said: Originally, I thought, that if anyone would tell me that the halachah agrees with R. Judah, that a blind person is exempt from the precepts,I would make a banquet for the Rabbis, seeing that I am not obliged, yet fulfil them. Now, however, that I have heard R. Hanina's dictum that he who is commanded and fulfils [the command] is greater than he who fulfils it though not commanded; on the contrary, if anyone should tell me that the halachah does not agree with R. Judah, I would make a banquet for the Rabbis. (Soncino translation)

Tosafot on the spot explains that the reasoning behind this is that an obligated individual goes through more worry and anguish that he might mess it up, while the non-obligated individual has nothing to worry about because he is not even obligated. The extra worry/anguish gets him extra reward.

נראה דהיינו טעמא דמי שמצווה ועושה עדיף לפי שדואג ומצטער יותר פן יעבור ממי שאין מצווה שיש לו פת בסלו שאם ירצה יניח

Ritva, in his commentary there, first quotes "our rabbis" as explaining that Satan goes after one who is commanded and not one who is not commanded. Therefore, one who is commanded receives more reward in accordance with the extra effort that was required.

פירשו רבותינו ז"ל טעם הדבר שזה שטן מקטרגו כשהוא מצווה וזה אין שטן מקטרגו ולפום צערא אגרא

He than quotes "our great rabbi" (Ramban) as explaining that one who is obligated fulfills the decree of the King by doing a mitzvah whereas one who is not obligated does not fulfill a decree of the King; hence the former gets more reward.

ורבינו הגדול ז"ל פירש שהמצות אינן להנאת האל יתברך המצוה אלא לזכותינו ומי שהוא מצווה קיים גזירת המלך ולפיכך שכרו מרובה יותר מזה שלא קיים מצות המלך

Answer 2

Alex focused on the question from the "from where" angle, I will talk about the "why" after the "/" in the title version of the question.

I think it makes sense from a-priori principles.

Why was this action obligated to this person, and this one left optional for that person? It would seem that the obligatory mitzvah is one that Hashem (in the case of deOraisa) or the Sanhedrin (in the case of deRabbanan) determined was more critical for this person to do.

In other words, logically speaking, it's not that the obligation directly or indirectly causes the reward. It is that the greater reward and the greater obligation are both consequences of the mitzvah's greater value to this particular person.

One can also read Tosafos in a manner consistent with this observation. They write:

נראה דהיינו טעמא דמי שמצווה ועושה עדיף לפי שדואג ומצטער יותר פן יעבור ממי שאין מצווה שיש לו פת בסלו שאם ירצה יניח

It appears this this is the reason: Someone who is commanded and does is greater because he is worried and troubled more, lest he violate [the command], compared to someone who was not commanded who has his "bread in his basket" [i.e. his needs are taken care of] so if he wants, he could rest.

While at first glance this Tosafos says that it's the command itself that causes the extra trouble which in turn causes the extra reward, they could be saying something very different. This read makes "pas besalo -- bread in his basket" an awkward use of the idiom. It implies that one has a need that the other already has met, not that the other never needed. Someone who is not commanded has "pas besalo", because they are deemed less lacking in this area. Which is the whole reason it wasn't put on their to-do list. Whereas someone who is commanded is commanded because the mitzvah is a growth experience and a challenge he must overcome. Thus, it takes him more work to avoid violating the command.

This is why the Ramban writes, "המצות אינן להנאת הקל יתברך המצוה אלא לזכותינו -- mitzvos aren't for the blessed G-d the Commander's benefit, but for our own merit." The one who is commanded and performed is one who needs that particular kind of merit. As the Ritva continues the thought, the commanded person's yeitzer hara is more active in this area than the non-commanded person. To explain: Which is the whole reason they didn't need the command.