Shemot 35:4-40:33 record the details of the construction of the mishkan. These details were already recorded by the instructions to build the mishkan, 25:1-31:11. Why was it not sufficient for the Torah to simply say the people did as Moshe commanded?
Nehama Leibowitz (1976a, pp. 644-653, see also Josipovici, 1988) reviews various answers to this question. She quotes the Ramban (on 36:8) that the repetitions “reflect the love and esteem with which the mishkan was viewed by G-d, the numerous recapitulations being designed to increase the reward of those engaged in (the study of) it.” However, she is not satisfied with this answer, and she wonders, “Why should this particular narrative be more highly valued than those conveying the very fundamentals of Judaism?” For example, was the mishkan more esteemed than the korban pesach? By the korban pesach, the Torah records all the instructions and afterwards just records that the people did as commanded, 12:28, without detailing all of their actions. A second approach is from the Ralbag (comments after chapter 40) and Cassuto (1967, p. 453) that the repetitions are just following the literary style of ancient times. N. Leibowitz is not satisfied with this approach and instead she prefers Moshe Mendelssohn’s approach in the Biur, who suggests that just as man dedicates his first fruits to G-d, so too the work in the mishkan represents the Jewish people’s “first fruits of their thoughts and abilities.” N. Leibowitz concludes that the repetition “was done in order to stress the symbolic significance of each detail, the dedication of each labor to G-d in preparation for life in the Promised Land.”
A different approach is that the repetitions have two messages and this can be seen by dividing the repetitions into two sections. The first section is from 35:4-36:7, and focuses on the donations to the mishkan, while the second section is from 36:8-40:33, and focuses on the actual construction of the mishkan.
The first section, 35:4-36:7, can be further divided into four smaller sub-units. The first of these sub-units, 35:4-19, records Moshe’s request to the people to donate materials to the mishkan, and includes a repetition of the list of the components of the mishkan including a mention of the priests’ clothing, 35:11-19. The Ramban (on 35:5) points out that the people had to be told this information before they were asked to make donations, as otherwise they would not have known what to donate, and usually when people know what the donations will be used for they give more generously.
The second sub-unit of the first section is 35:20-29 records in detail all the donations of the people. The third sub-unit of first section is 35:30-36:1, records the appointments of Betzalel and Oholiav to be in charge of building the mishkan. This seems to essentially repeat 31:1-11, but this is the first time the people are hearing about Betzalel and Oholiav. The people had to hear that G-d selected Betzalel and Oholiav in order that they would accept them as being in charge, and 36:1 records that everybody worked together. The fourth sub-unit is 36:2-36:7, which records that Moshe found out that the people had donated more materials than were needed for the mishkan, and he told them to stop donating.
The point of the section from 35:4-36:7 is the bigheartedness of the people in their donations to the mishkan. As noted by the Midrash (Shemot Rabbah 48:6, see also N. Leibowitz, pp. 666-668) through these donations the people expiated their sin by the golden calf. The people had donated gold to the make the golden calf, and the people redeemed themselves by donating much greater quantities of metals and other materials to the mishkan. This lesson was so important that the Torah had to dwell at length on the donations, as it does by the donations of the people after the war with Midyan, Bemidbar 31:25-54. This lesson might have been missed if the Torah simply stated that the people donated what they had been asked to donate. (Note even though the donations to the mishkan expiated the sin of the golden calf, this does not mean that the mishkan itself was because of the sin of the golden calf, see our discussion on 30:1-10, "The barriers arise," https://lobashamayim.blogspot.com/2011/02/shemot-301-10-tetsavveh-barriers-arise.html)
The second large section is from 36:8-40:33 and can be further divided into five sub-units. One, 36:8-38:20 records the construction of the items and the walls of the mishkan. Two, 38:21-31, gives an accounting of the metals used in constructing the mishkan. Three, 39:1-32, records the making of the priests’ clothes. (Note, 39:1 is a connecting sentence between the accounting section of 38:21-31 with the making of the priest’s clothing, as it gives an accounting of the dyes used to make the priests’ clothing.) Four, 39:33-43 records that after all the items of the mishkan were finished the people brought them to Moshe. (Are 39:32 and 39:43 bookends?) Five, 40:1-15 records, for the first time, G-d’s instruction to Moshe to assemble the mishkan and 40:16-33 records that Moshe fulfilled these instructions. Note, 40:16 functions both as a concluding sentence to the instructions that they were fulfilled and as an introduction to 40:17-33, which records in detail how Moshe followed the instructions. Also, 40:16-33 does not record that Moshe fulfilled all of G-d’s instructions in 40:1-15, as some of this fulfillment is recorded in Vayikra chapter 8 and some in Bemidbar chapter 7, see our discussion on 40:1-33, “The anointing of the mishkan” (https://lobashamayim.blogspot.com/2010/03/shemot-401-33-pekudei-anointing-of.html).
One phrase that appears repeatedly in the section 36:8-40:33 is "he built" or "they built." This suggests that the crucial aspect of the repetition is to stress the work that was done. This section focuses on the work of the people, and the last sub-unit even records that Moshe, the man who came closest to G-d of any human being, also participated in building the mishkan. The fact that the Torah records with such details the building of the mishkan must surely indicate the importance the Torah attaches to this activity. Thus, Ramban (end of comments on 36:8) explains that the Torah recorded the details of the people’s work to show how much G-d desired their work.
Rabbi Tarfon (end of 1st century) made this same point regarding the importance of work from a different perspective. He stated (Avot de-Rav Natan, 11:1) "Even the Holy One, blessed be He, did not cause His Presence to dwell in Israel until they had performed some work (translation from Cashdan, 1965, p. 67). Yeshayahu Leibowitz (1990, pp. 85,91) explains that the “dwelling” of G-d came about as the result of the work of men since there was no overt Divine intervention or miracles in the construction of the mishkan.
Furthermore, there are several literary connections between the mishkan and the creation of the world both by the instructions to build the mishkan and by the conclusion of the building of the mishkan. With regard to the instructions, they can be divided into seven sections based on the opening phrase, G-d spoke to Moshe, 25:1, 30:11, 30:17, 30:22, 30:34, 31:1 and 31:12, see Sarna, 1999, p.201. The seventh section discusses the laws of Shabbat and references the creation of the world, 31:17. The sixth section records the appointment of Betzalel and Oholiav to build the mishkan, and this corresponds to the sixth day of creation since in both cases the focus is on humankind. There is even a similarity between the blessings, as on the sixth day man is created in the image of G-d, Bereshit 1:27, and 31:3, within the sixth section, records that G-d filled Betzalel with the spirit of G-d.
With regard to the completion of the mishkan, Cassuto (1883-1951, pp. 476, 477, 483) points out four parallels between the mishkan and the creation of the world. One, 39:32 records that all the work of the mishkan was completed and this is similar to Bereshit 2:1 which records that on the seventh day, the world was completed. Two, 39:43 records that “Moshe saw all the work” and this seeing is reminiscent of the seeing of G-d by creation, Bereshit 1:31. Three, 39:43 also records that Moshe blessed the people, which parallels that G-d blessed the seventh day after the creation of the world, Bereshit 2:3. Four, 40:33 records that Moshe completed the work, which is parallel to Bereshit 2:2 that on the seventh day G-d completed His work in creating the world.
The creation of the world and the building of the mishkan are the two great creative acts in the Torah, the first by G-d and the second by mankind. These literary connections between these two acts indicate the importance of the work of the Jewish people in building the mishkan.
Accordingly, maybe the point of the section, 36:8-40:33, is to emphasize the importance of working and creating. The mishkan is the great building project of the Torah where the people took all the different materials and fashioned them into a purposeful construct. The building of the mishkan was a fulfillment of the prime directive to humankind to conquer the world in Bereshit 1:28. The building of the mishkan is the only, or the best opportunity, in the entire Torah to stress this point, and this lesson would have been lost if the Torah had merely stated the people did as they were commanded without recording all the details of the work.