Right after the sin of the meraglim we have the parsha of nesachim and the mitzvah of challah. The Midrash comments as follows:
In other words, nesachim and challah were a sign that “kvar ratzah Elokim es ma’asecha” (as the pasuk in Koheles ends), of G-d’s acceptance of the Jewish people despite their failings.
The Ishbitzer points out that the pasuk in Koheles first refers to bread and then to wine, yet the order in the Torah is reversed – first we have the parsha of nesachim, which involves pouring wine on the mizbeyach, and then afterwards we have the parsha of challah, which is taken when baking bread. Why does the Torah reverse the order from the order in Koheles?
Challah represents yiras shamayim, wanting to be extra careful and go the extra mile for G-d. The farmer already took out terumah, took our ma’aser, took out ma’aser sheni or ma’aser ani – he’s shown that he remembers that his crops are dependent on G-d. Now he comes to bake his bread and he’s still not satisfied – let’s take off one more portion and give it to the kohen just to be safe.
Nesachim represent the depths of the heart. The gemara in Sukkah tells us that the wine poured on the mizbeyach went down a hole straight into the deepest depths of the earth.
In an ideal world challah comes before nesachim, we would build up our yiras shamayim until we felt it penetrate down into the depths of the soul.
Post-cheit hameraglim is what happens when the the ideal has been shattered. You can’t talk about building up yiras shamayim until it penetrates down into the heart if you think, “heimasu es levaveinu,” that the heart is completely corrupt and unredeemable. The Torah therefore reverses the order. First comes the parsha of nesachim – there is still something down there in the depths that can be reached. The cheit of a Jew is only on the surface and never fully corrupts the soul. Once Klal Yisrael absorbed that lesson and believed that they still had a connection, then the Torah gives the parsha of challah and talks about rebuilding yiras shamayim.
The gemara (Brachos 14) says that a person who reads kri’as shema without tefillin is like a person who offers a korban without the nesachim that go with it. What’s the comparison? When a person wraps tefillin around his head and his arm he shows that his mind and heart and the actions he takes with his hands are all connected – what he is saying is part of how he thinks, acts, and feels; it’s not just words coming out of his lips. In light of the Ishbitzer perhaps the gemara means that just as the nesachim drip down to the deepest depths, it’s the donning of tefillin that shows that the message of shema is part of the essence of the person. (See Shem m’Shmuel for a different interpretation.)