Four parashot in the Book of Exodus describe the construction of the Mishkan (Tabernacle) and its furnishings: Terumah and Tetzaveh detail God's commands to Moses regarding the construction, while the parashot Vaiyakhel and Pekudei deal with Moses' command to the people and the details of the construction. Thus begins the parashah Vaiyakhel: Moses gathers all the people of Israel and conveys to them the words of God: "Take from yourselves an offering to God...gold, silver, and copper." Then the parashah recounts the construction of the Mishkan, and in the parashah Pekudei, the completion of all the work is recounted.
However, these parashot are not written in an uninterrupted sequence: there is a parashah that separates the Divine command from its practical implementation. This parashah, Ki Tisa, comes after Terumah and Tetzaveh and before Vayakhel and Pekudei, where other matters are described.
Furthermore, not only does the parashah Ki Tisa not contain matters related to the construction of the Mishkan, but it also recounts events that are completely contrary to the concept and purpose of the Mishkan and the dwelling place of God on earth. The main story of the parashah Ki Tisa is the sin of the Golden Calf, a sin that all generations, including our own, still strive to correct and suffer for.
It is well known that everything in the world happens by Divine Providence, that is, for a specific reason and purpose established by God. This rule applies not only to the events themselves but also to the order in which they occur. If this is so, why did God place the story of the Golden Calf right in the middle of the parashot that describe the construction of the Mishkan?
Herein lies an important teaching on the service of every Jew to God. The work of building the Mishkan, as recounted in the Torah in these parashot, symbolizes the work of every Jew to make himself and the world around him a dwelling place for the Divine Presence. God commands every Jew: "Build a Temple for Me, and I will dwell within it," within each one of them—the Jewish people.
It can happen that between the Divine command and its practical implementation, matters arise that hinder the fulfillment of God's Will. The Yetzer Hara—the evil inclination—can enter and draw the person toward matters that are completely contrary to the purpose of the Mishkan.
On the other hand, when the Divine command descends and is delivered by Moses, the words are put into practice immediately, without interruption from other matters (as we see in this parashah, where the construction of the Mishkan begins after Moses' command). Even if the Yetzer Hara tries to interfere and cause problems, it can only delay the construction of the Mishkan for a few days, but in the end, it will be successfully completed.
The mandate transmitted by Moshe in his time, as well as the Moshe of each generation, as explained in Kabbalah, that there is a Moshe in each generation, has the force of a promise, that the mandate will be fulfilled and the Jewish people will carry out the Divine Will and reach the point where "the Glory of God fills the Mishkan.".
This is the symbolism behind the parashot Vaiakhel and Pekudei being read together in most years, to show that there is no interruption between Moshe's command and the completion of the work of building the Mishkan in practice.
Adapted from Shulchan Shabbat.