Fourth of the Thirteen Principles of the Jewish Faith laid down by the Rambam in the twelfth century, and the fourth of five principles relating to the Existence and Nature of G-d:
“I believe with complete faith that the Creator, Blessed is His Name, is the very First and the very Last.”
The Torah refers to G-d as the “Creator,” the “First Cause” or the “First” in its very first verse:
“In the Beginning, G-d created Heaven and Earth.”
In the Shirat HaYam, Moshe and the Children of Israel sing, “HaShem will be King forever”(Shemot 15:18). And at the end of his life, Moshe sings, “Above is the abode of the Most Ancient G-d, and Below are His Eternal Arms” (Devarim 33:27)
In the Prophets, we find explicit reference to G-d as the “First” and the “Last:”
“Who has wrought and done it? Calling the generations from the beginning? I, the L-rd, the First, and with the Last, I am He.” (Yeshayahu 41:4)
And again, “Thus says the L-rd, the King of Israel, and its Redeemer, the L-rd of Hosts; I am the First, and I am the Last; and beside Me, there is no G-d.” (ibid. 44:6)
And yet again, “Listen to Me, Yaakov, and Yisrael, whom I have called, I am He; I am the First, and I am also the Last.” (ibid. 48:6)
In the “Mishne Torah” of the Rambam, we find, “The Foundation of Foundations and the Pillar of all Wisdom is to know that there was One Who existed First. And He brought everything else into being. And everything that exists in Heaven and Earth and the space that is between them exist only by the Truth of His Existence.” (“Hilchot Yesodei HaTorah,” “Laws Concerning the Foundations of the Torah” 1:1). And the Rambam sees the fact that HaShem is also the “Last” as a consequence of the Principle of Incorporeality [“Ani Maamin-3”]: “…And if the One Who Formed Everything were Corporeal, He would have Finality and an End, for it is impossible for there to be anything physical that has no end…” (“Hilchot Yesodei HaTorah,” 1:7)
The poetic rendition of this Principle in the “Yigdal” Prayer is as follows:
“He preceded every being that was created –
The ‘First,’ and nothing precedes His Precedence.”
Oddly, there is no explicit reference here in “Yigdal” to HaShem’s being the “Last” as well, except that in the first stanza [related to “Ani Maamin-1”], the text reads, “…unbounded by Time is His Existence.”