Midras Keluaran 18:12: Mekhilta DeRabbi Yishmael, Pesikta Rabbati, Midrash Tanchuma Buber & Vayikra Rabbah

(Exodus 18:12) "And Yithro, Moses' father-in-law took a burnt-offering and peace-offerings (for sacrifice) to G–d.": Scripture registers wonder here: A man who had worshipped idolatry and who had poured libations and bowed down to idolatry now brings a burnt-offering and sacrifices to G–d!

… it is written there “Behold the heaven and the heaven of heavens cannot contain You…” (Melachim I 8:27) and here it is written “…the glory of the Lord filled the Tabernacle.” (Shemot 40:35) R’ Yehoshua of Sachnin said in the name of R’ Levi ‘to what is this likened? To an open cave at the edge of the sea. When the sea storms the cave is filled, but the sea is not reduced. So too, even though it is written that ‘the glory of the Lord filled the Tabernacle’ the upper and lower worlds did not lose anything of the brilliance of the glory of the Holy One, just as it is written “Do I not fill the heavens and the earth? says the Lord.” (Yirmiyahu 23:24) Therefore it is written here ‘And it was’. Just as the Divine Presence was here below at the beginning of the creation of the world but withdrew to above, now it returned to be below as it had been “And it was that on the day that Moses finished…” (Bamidbar 7:1) ... [Another explanation. “And it was that on the day that Moses finished erecting the Mishkan…” (Numbers 7:1)] R’ Simon said: at the time when the Holy One told Israel to erect the Tabernacle, He hinted that when the Tabernacle below is erected, the Tabernacle above is erected, as it says “And it was that on the day that Moses finished…” (ibid.) It does not say ‘erecting the Tabernacle’ but rather ‘erecting this (et) the Tabernacle.’ This refers to the Tabernacle above. The Holy One said: in this world, when the Tabernacle was erected, I commanded Aharon and his sons that they bless you. In the time to come I, in my glory, will bless you. So it is written “May the Lord bless you from Zion, He Who made heaven and earth.” (Psalms 134:3)

(Exod. 18:5–6:) NOW JETHRO, MOSES' FATHER-IN-LAW CAME…. AND HE SAID UNTO MOSES: I AM YOUR FATHER-IN-LAW…. Who said to Moses: I AM YOUR FATHER-IN-LAW? He was unable to come to Moses. What did he do? He wrote a letter and tied it on an arrow. Then he shot, and the arrow came to Moses. Moses read it and went out to him, as stated (in vs. 7): SO MOSES WENT OUT TO MEET JETHRO. He entered the camp along with him. What is written (in vs. 12)? AND AARON CAME WITH ALL THE ELDERS OF ISRAEL TO EAT BREAD <BEFORE THE LORD WITH MOSES' FATHER-IN-LAW >. When they had eaten with him, he said: Give me permission to go to my <own> place. Moses said to him (in Numb. 10:32): IT SHALL BE THAT, IF YOU COME WITH US, IT SHALL COME TO PASS THAT WHATEVER GOOD THE LORD DOES FOR US WE WILL DO FOR YOU. <Jethro> said to him: I want to go and utter the Holy One's praise in my own place. Immediately (in Exod. 18:27): MOSES SENT HIS FATHER-IN-LAW AWAY…. Now when the Holy One does miracles for Israel, they praise him [and the nations of the world praise him]. Thus it is stated (in Ps. 138:4): {THESE PEOPLES} ALL THE KINGS OF THE EARTH SHALL GIVE THANKS TO YOU, [O LORD,] FOR THEY HAVE HEARD THE WORDS OF YOUR MOUTH.