Parshas Ki Sisa begins with the commandment to raise up the heads of the people of Israel by having them contribute a half shekel of silver. How does this contribution raise them up?
The phases of the Mishkan had involved first raising up Aharon as the Kohen Gadol, then the Kohanim as a whole, then the sons of Levi, each Kiper uplifting the designated group to a new higher state. This was the turn of the Jewish people as a whole.
As the Kohanim were analogous to the Kodesh HaKedeoshim, the Leviim were analogous to the interior of the Mishkan whose vessels they bore on their shoulders, the people of Israel were analogous to the walls of the Mishkan itself, creating the border and boundary of the House of G-d.
So the Jewish people were raised up by contributing the half-shekel of silver. This silver was used to form the sockets that held the beams that formed the wall of the Mishkan. So while the Kohanim and Leviim might minister within it, it was the Jewish people who were its walls. With them there was a House of G-d. Without them there was no house.
And the amount was designated as half a shekel because it was not the individual contribution that counted, but the willingness to join with each other. Together they formed the people. Just as each wooden plank alone formed nothing, so too alone we are only individuals. It is together that we have form and substance.
But the half shekel had a larger meaning as well. Because in the aftermath of the revelation of Har Sinai, the overwhelming experience left open the question for the Jews of how to connect to G-d. They had seen and heard incredible things, but those things seemed to them beyond their ability to relate to. G-d as they understood existed in a spiritual state, they existed in a physical one, and there was no bridge between them.
So when Moshe ascended the mountain, they came to believe that he would not return, because to reach such a high state was to be cut off from the physical world. And so in despair instead they turned to the gross physical deities of Egypt again.
But the silver half-shekel, as well as the sacrifices and the shalos regalim, showed them how the physical could be made spiritual. The silver half-shekel upholding the atzei shitim omdim, the acacia wood planks standing, turned their physical substance into an act of holding up the walls within which the spirit of G-d resided.
But what does one do when one has fallen too low to have the chance to physically connect to G-d in that way? As the greatest of prophets, Moshe could speak to G-d, Panim el Panim, face to face. When the Beit Mikdash stood, the Jewish people could visit and bring their first fruits and sacrifices up to G-d's "face", as it says, Velo Yerau Panai Reikam. But what about when this isn't possible?
The sin of the Het HaEgel demonstrated another way through Moshe's pleading. When G-d agrees to show him His glory, He places Moshe in the cleft of the rock. Vesmticha Benikrat HaTzur. Just as a moment before He says, VeKarati BeShem Hashem. The cleft of the rock in which Hashem places Moshe is Tefila, prayer.
Even when the Jewish people had sinned and were not worthy of seeing the face of G-d, they could reach the Tzur that is Hashem through the cleft through which Tefilot travel. And in doing so they might not see His face, but they would see Him from behind and gain his mercy.
Thus Hashem taught Moshe the Shalosh Esra Midot, the Thirteen Midot, which begin with the double repetition of Hashem's name. The first is to indicate that he is a merciful G-d before man sins. The second that he is merciful even after the sin. And though in this state man may not be able to see "His Face", but they can still reach him and gain his mercy.
Thus Parshas Ki Sisa serves as an education in how to reach G-d. Its beginning shows how to see his face by physically contributing to the projection of his presence on earth. Its conclusion shows how to reach him even when we cannot see him, through the cleft of the rock, in prayer. By these two means, the Jews were taught how to bridge the realm of G-d with their own.