Foolish Galatians, who has bewitched you not to obey the truth, before whose eyes Yeshua the Messiah was openly set forth among you as crucified?
I just want to learn this from you. Did you receive the Spirit by the works of the law, or by hearing of faith?
Are you so foolish? Having begun in the Spirit, are you now completed in the flesh?
Did you suffer so many things in vain, if it is indeed in vain?
He therefore who supplies the Spirit to you, and works miracles among you, does he do it by the works of the law, or by hearing of faith?
Even as Abraham believed God, and it was counted to him for righteousness.
Citing Genesis 15:6,
וְהֶאֱמִן, בַּיהוָה; וַיַּחְשְׁבֶהָ לּוֹ, צְדָקָה.
“And he believed in HaShem, and it was counted to him as righteousness.”
The Mekhilta de’Rabbi Ishmael makes the same point, using the same verse,
“Great indeed is faith before Him who spoke and the world came into being. For as a reward for the faith with which Israel believed in God, the Holy Spirit rested upon them and they uttered the song as it is said: “And they believed in the Lord….Then sang Moses and the children of Israel” (Ex. 14.3; 15.1). R. Nehemiah says: Whence can you prove that whosoever accepts even one single commandment with true faith is deserving of having the Holy Spirit rest upon him? We find this to have been the case with our fathers. . . you find that our father Abraham inherited both this world and the world beyond only as a reward for the faith which he believed, as it is said: “And he believed in the Lord,” etc. (Gen 15.6). And so also you find that Israel was redeemed from Egypt only as a reward for the faith with which they believed, as it is said: “And the people believed” (Ex. 4.31).”
Mekhilta de-Rabbi Ishmael, Tractate Beshallah, Volume I, translated by Jacob Z. Lauterbach, PhD, Jewish Publication Society, pg. 167