BISHALACH - NO FREEBIES
The Chidah writes that Klal Yisrael said מן הוא - מ'עשה נ'יסים הוא - not knowing if they could benefit from it being that it was supernatural. Moshe responded
הוא הלחם - it is THE bread that you are familiar with - a consequence of Avraham's לחם that was offered to his "guests". Since the bnei Yisrael were cared for in the wilderness as a result of Avraham's hosting, it was a payment that was due to them and they could benefit from it.
(The Chanukas HaTorah points out that Avraham didn't even actually end up serving the bread! As we know it became unfit when Sarah already saw her youthful "nature" return. But Avraham's thought was rewarded as if it was fulfilled, and the Manna had this quality as well, in which the thoughts of the one eating it would have practical implications in its taste and texture.)
The question arises though, that since when was it a problem to benefit from the miracles occurring to the Jews then? They had a myriad of miracles during the plagues of Mitzrayim, the clouds of glory, numerous miracles at Yam Suf, and most recently and similarly the miraculously sweet waters of Marah! Why now was there an issue with the manna?
There is an eye opening Mechilta that speaks about the waters of Marah. R' Eliezer says that the waters were originally perfectly palpable and only upon their arrival did it turn bitter. Why? כדי ליגען - Specifically to tire and weaken them! Another Tanna states that even the water that they had in their own flasks drained or turned bitter! The medrash relates that this was "payback" for taking fresh water in the split Yam Suf.
We see from here that from the yam suf and on Hashem introduced a new manner of Hashgacha upon Klall Yisrael and the world at large. The Maharal writes of the difference between the 10 ma'amaros of creation and the transition to the 10 dibros at mattan Torah. The "soft spoken" approach was in use for thousands of years as part of Olam Chesssed Yiboneh, with no real merit to keep the world deserving of its existence. תולה ארץ על בלימה. But the goal was to get to mattan Torah when then there would be definite expectations from humanity. As dibbur is a form of speech that demands and leads to a response.
Similarly the Ruach Chaim writes that the 10 complaints of the Jews against Hashem in the wilderness are only from Krias Yam Suf and on, but the requests (see Rashi in quoting Avos D'R' Nosson about their requests before entering the sea.) and complaints until they entered the waters were all dismissed. This is because until then they were ביד רמה in a state of exultant confidence as they left Mitzrayim - and as a "spoiled" child there was no expectation of them being humbled and disciplined. But ויענך וירעיביך - at some point, which we are suggesting was as they actually crossed the sea - began a new period of עינוי, a humbling discipline of exercises to develop Klal Yisrael into a fully responsible nation living with tremendous expectations of them.
"Paying" for their water was their first experience of accountability.
According to the medrash that they had not learned Torah for three days, there was clear sign that as Jews, even water cannot be taken for granted. Torah is literally our spiritual AND PHYSICAL sustenance. As the Mishnah says in Avos הכל נתון בעירבון - everything is given on credit. Every single thing we enjoy, and even our basic living conditions, must be "paid for" in full at some point in time. And as is well known from Yisrael Salanter, the world is an expensive hotel. Nothing is free and everything is expensive.
Perhaps these lines leave a bit of bitterness in our mouths, but that is what Marah was meant to convey.
But there is a way around it. Klall Yisrael experienced the most awesome miracles at the time but instead of their response being full of love it seems to have remained on the level of וייראו העם את ה' - They FEARED Hashem. In a relationship of fear, all is "din" all the numbers must add up and there is no room for deviation. However, as the Rambam writes in Hilchos Teshuvah and many others as well, when one serves Hashem out of love there are many freebies indeed. Like a loyal employee who has his business lunch paid for by the firm, when someone is dedicated to serving Hashem באהבה , his Boss takes care of him pro bono. These are the promises we find in the Torah for material success, health and peace as they are all there to enhance the dedicated service of the loyal employee.
ראה אנכי נותן לפניכם היום....
ובחרת באהבה