The Rishonim have different opinions regarding which events in the Torah are written in chronological order and which are not. According to those who hold that events in the Torah are not necessarily presented in chronological order, there still must be a reason why the Torah would go out of its way to change the order when it does.
In the beginning of Parashat Ki Tisa, the Torah describes Bnei Yisrael’s donations of vessels and money, which will be used towards the building of the Mishkan. Right after mentioning the Shemen Mishchat, the anointing oil, and the Besamim, the incense spices (Shemot 30:22-26, 31:1-11), Hashem tells Moshe to tell Bnei Yisrael to be careful about observing Shabbat (31:12-17). This sudden change in topic is difficult. Why does the Torah jump from describing what is needed in the Mishkan to talking about the observance of Shabbat? It seems to be out of order.
Many commentaries say that the Torah mentions Shabbat here because the building of the Mishkan was not permitted to interfere with Shabbat observance. Shabbat is so important because it represents the special relationship between Am Yisrael and Hashem. Even though we are extremely excited about the Mishkan, we cannot let our enthusiasm override our commitment to Shabbat.
However, there is an additional message. Just as the Torah seems to interrupt the description of the Mishkan to emphasize the importance of observing Shabbat, the Navi in Melachim I seems to interrupt the description of the building of the Beit HaMikdash to ensure Shlomo follows the Mitzvot. Hashem suddenly tells Shlomo HaMelech that if he keeps the Mitzvot, Hashem will live amongst Bnei Yisrael. This implies that if Shlomo is not careful to keep the Mitzvot, Hashem will not live amongst Bnei Yisrael, and the Beit HaMikdash will have been built for nothing (Melachim I 6:12-13). The success of building a home for God depends on how loyal we are to Him.
At the completion of the building process, all of the wonderful things that had been donated and crafted for the Mishkan will only matter if Bnei Yisrael keep the Mitzvot and are loyal to Hashem.
It is important for all of Klal Yisrael to act with intentions of being close to Hashem and having the proper mindset towards Mitzvot. We may buy many objects such as Talitot and Tefilin, but what really makes the Mitzvah so special is our personal connection and loyalty towards Hashem.