(1) Moses then gathered the whole Israelite community and said to them: These are the things that יהוה has commanded you to do: (2) On six days work may be done, but on the seventh day you shall have a sabbath of complete rest, holy to יהוה; whoever does any work on it shall be put to death.
As asked by many of the sages of Israel, why is the instructing to build the Tabernacle and the commandment to Keep the Shabbat sandwiched together in one grouping? One approach is the following, based on whats written in the Book of Daniel -
(24) Therefore, O king, may my advice be acceptable to you: Redeem your sins by charity and your iniquities by generosity to the poor; then your serenity may be extended.”
Based on this above verse (That giving charity redeems one from his/her sins), all the while a person has not repented for his/her sins, then the charitable act of giving to the poor is not considered a Mitzvah (commandment) of giving Tzedaka (charity). This would be the case since the charity you are giving clears you of your sins, so it would seem you aren't giving for the sake of giving, rather you are giving to remove your iniquities from you, which is for you and not for the sake of the commandment of giving charity!
As we can see below, there is a concept of man that only gives to save his own life.
(4) The Adversary answered the LORD, “Skin for skin-a—all that a man has he will give up for his life.
So what this person is giving, is really for himself. That being the case, let us look into the scenario when the Children of Israel worshiped the Golden Calf. They were afterwards instructed to build the Mishkan (Tabernacle) in order to atone for the Sin of the Golden Calf, as it is taught below by Rashi -
Based on all of this, how is it possible to say that what was contributed by the Israelites towards the building of the Tabernacle is called a donation (Nedava in Hebrew)? As we see this language being used in the below verse -
דַּבֵּר֙ אֶל־בְּנֵ֣י יִשְׂרָאֵ֔ל וְיִקְחוּ־לִ֖י תְּרוּמָ֑ה מֵאֵ֤ת כׇּל־אִישׁ֙ אֲשֶׁ֣ר יִדְּבֶ֣נּוּ לִבּ֔וֹ תִּקְח֖וּ אֶת־תְּרוּמָתִֽי׃
Tell the Israelite people to bring Me gifts; you shall accept gifts for Me from every person whose heart is so moved.
Wasn't the above mentioned donations set in place only to atone for the Israelites? So how does HaShem call them gifts and donations!?
And let us answer this question with the help of Heaven based on this teaching from the sages of Israel -
אָמַר רַבִּי חִיָּיא בַּר אַבָּא אָמַר רַבִּי יוֹחָנָן: כׇּל הַמְשַׁמֵּר שַׁבָּת כְּהִלְכָתוֹ, אֲפִילּוּ עוֹבֵד עֲבוֹדָה זָרָה [כְּדוֹר] אֱנוֹשׁ — מוֹחֲלִין לוֹ, שֶׁנֶּאֱמַר: ״אַשְׁרֵי אֱנוֹשׁ יַעֲשֶׂה זֹּאת וְגוֹ׳ מֵחַלְּלוֹ״. אַל תִּקְרֵי ״מֵחַלְּלוֹ״ אֶלָּא: ״מָחוּל לוֹ״.
Rabbi Ḥiyya bar Abba said that Rabbi Yoḥanan said: With regard to anyone who observes Shabbat in accordance with its halakhot, even if he worships idolatry as in the generation of Enosh, God forgives him
If so (that Shabbat atones for sins), after Israel kept their first Shabbat as commanded, the Sin of the Golden Calf was atoned for and forgiven, and there was then no further need for the mechanism of charity to atone for their sins, and in that regard it does make sense that their gifts towards the Tabernacle could actually still be called a donation. And based on this, it can be understood why our Holy Torah put the reality of Shabbat directly before the building of the Tabernacle, because through keeping the Shabbat, a persons sins are forgiven, and that being the case, the Israelites were already forgiven for the Sin of the Golden Calf prior to the donations and dedications to the Tabernacle, and as a result, the donations towards the Tabernacle can actually have the reality of it being considered a gift.