Midras Bilangan 15:14: Shemot Rabbah & Sifrei Bamidbar

Another matter, “all the wise hearted,” that is what is written: “I am black but comely” (Song of Songs 1:5). If black, why comely? Is there one who is black and comely? Rather, the congregation of Israel said: ‘I am black in my actions, but I am comely in the actions of my ancestors. I was black in Egypt, but I was comely when I said at Sinai: “Everything that the Lord speaks we will perform and we will heed” (Exodus 24:7). I was black at the sea, as it stated: “They were defiant at the sea, the Red Sea” (Psalms 106:7), but I was comely when I said: “This is my God and I will exalt Him” (Exodus 15:2). I am black due to the crafting of the calf, but I am comely due to the crafting of the Tabernacle. I am black with a bull, as it is stated: “They exchanged their Glory for the image of a bull” (Psalms 106:20), but I am comely with a bull, “a bull, a lamb, or a goat” (Leviticus 17:3). I am black in the Tabernacle, as it is stated: “They defiled My Sanctuary” (Ezekiel 23:38), but I am comely in the Tabernacle.’
“All the wise hearted…crafted.” What labor did they perform? See what is written: “This is the gift [teruma] that you shall take from them: [Gold, silver, and bronze]” (Exodus 25:3). This is the congregation of Israel, which is a gift, as it is stated: “Israel is sacred to the Lord, the first of His crop” (Jeremiah 2:3).²Teruma taken from produce is also referred to as the first of the crop (e.g., Numbers 18:11–12). “Gold and silver,” this is the congregation of Israel, as it is stated: “Wings of the dove covered with silver, [its pinions with green and gold]” (Psalms 68:14). “And bronze,” this is the Land of Israel, as it is stated: “And from its mountains you will hew bronze” (Deuteronomy 8:9). “Sky blue [wool],” this is the congregation of Israel, as it is stated: “They shall place on the fringe of the corner a sky blue thread” (Numbers 15:38). “Purple [argaman], and scarlet wool [tolaat shani],” this is the congregation of Israel, as it is stated: “Fear not, worm [tolaat] of Jacob” (Isaiah 41:14), and likewise: “Your lips are like a scarlet thread” (Song of Songs 4:3). And it says: “The princes of Judah in their throng [rigmatam]” (Psalms 68:28).³Thus, the labor was to understand the hidden significance in each detail of the Tabernacle, as in the examples cited here in the midrash. Alternatively, the people of Israel themselves were meant to be the primary address of the Divine Presence, and the job of those performing the labor was to prepare them to be absolutely dedicated to divine service (see Etz Yosef; Midrash HaMevoar).
Another matter, “gold,” this is Abraham, who was tested in the fiery furnace like gold. “And silver,” this is Isaac, who was purified like silver upon the altar. “And bronze [neḥoshet],” this is Jacob, as it is stated: “I have divined [niḥashti], and God has blessed me on your account” (Genesis 30:27).

(Bamidbar 15:14) "And if a stranger sojourn among you": This tells me (as being likened to an Israelite in this regard) only of a proselyte who had converted before (i.e., one who had left Egypt with them). Whence do I derive (the same for) one who converts now? From "and who shall be in your midst throughout your generations." "and he shall offer a fire-offering": kinds of blood (i.e., animal sacrifices involving blood). You say sacrifices involving blood, but perhaps only a meal-offering (which is entirely burned)! — It is, therefore, written "Thus shall he do." Just as you (in the desert offered) kinds of (sacrifices involving) blood, so, converts offer kinds of blood. — (In that case,) why should we not say: Just as Israel (in the desert offered) blood of a beast ([and not of a fowl] viz. Shemot 24:5), so, converts (are inducted only) through the blood of a beast. It is, therefore, written (Bamidbar, Ibid. 16) ("One Torah and one judgment shall there be) for you (and for the stranger who sojourns with you") — To you (in general, as requiring blood for induction into Israel) have I likened him and not to (the specifics [i.e., beast versus fowl] of) your offerings. Rebbi says: Just as Israel entered the covenant only with three things — circumcision, immersion, and acceptance of the offering — so, the proselytes, like them. — But perhaps just as Israel through peace-offerings, so, proselytes, through peace-offerings. It is, therefore, written "And he shall offer a fire-offering, a sweet savor to the L-rd." Come and see: Which kind of blood (sacrifice) is relegated entirely to the fire, nothing remaining of it? Only a fowl burnt-offering ([but in a beast burnt-offering, the skin reverts to the Cohanim]). I might think (that the induction of the proselyte can be satisfied) even with a meal-offering; it is, therefore, written ("As you are) thus (shall the stranger be"). To bring one bird (as a fowl burnt-offering) is impossible. For we do not find a single bird serving as an offering in the entire Torah — whence it was stated: All the bird couples in the Torah — half is a burnt-offering; half a sin-offering, except for that of a proselyte, which is entirely (relegated) to the fire. Variantly: "As you do, thus shall he do": What is the intent of this? For it would follow (otherwise), that since we find the Torah to have differentiated his offering, (Israel bringing [beast] burnt-offerings and peace-offerings, and a proselyte, a fowl burnt-offering), it is, therefore, written "Just as you do (with libations), thus shall he do" — Just as you, six (logs) for a bullock, four for a ram, and three for a lamb, thus the proselytes."