Gen 17:5

“However, a question arises here which should not be passed over and which may perhaps also, quite independently, be bothering some of you. What does it mean, that when the name of Abraham, this man Jacob's grandfather, was changed (he was previously called Abram, you see, and God changed his name and said, you shall not be called Abram, but Abraham)? From that time on he was never called Abram. Search in the Scriptures, and you will see that earlier on, before he received another name, he was only called Abram. After he had received the new one, he was only called Abraham. This man Jacob, however, heard the same words when he received another name: You shall not be called Jacob, but you shall be called Israel. Now search the Scriptures, and see how he was always called either name, both Jacob and Israel. When Abram got another name, he was never called anything but Abraham; when Jacob got another name, he was called Jacob and Israel. The name Abraham was to receive its explanation in this world, because it was here that he became the father of many nations, from which his name is derived. The name Israel, on the other hand, belongs to the next world, where we will see God. So the people of God, the Christian people, is in this world and this time both Jacob and Israel; Jacob in our actual situation, Israel in our hopeful expectation.”

“כי אב המון גוים FOR A FATHER OF A MULTIDUDE OF NATIONS — An acrostic on his name [אב (ר) הם]. But the ר which was previously in his name — denoting that he was the father (chieftain) only of אב (א) רם] ארם] which was his native country (cf. Genesis 21:7 with verse Genesis 21:10 of the same chapter), whilst now he became father of the entire world — nevertheless was not taken out of his name. For we find also, that the 'י in Sarai’s name continued to complain to God that it had been removed from her name when this was changed to Sarah, until it was placed as an additional letter into the name יהושע, as it is said, (Numbers 13:16) “And Moses called Hoshea (הושע) the son of Nun, Joshua (יהושע)” (Genesis Rabbah 47:1).”

“Neither shall thy name be any more called Abram,.... Which signifies an "high father", which name he bore for many years before he was the father of anyone: but thy name shall be Abraham: with all addition of the letter inserted into it, and makes the last syllable two, "raham": which word in the Arabic language, as Hottinger (g) observes, signifies "numerous" (h); so that with this addition his name Abraham may be interpreted, the father of a numerous offspring; and with this agrees the reason of it, as follows: for a father of many nations have I made thee; not that he was so already in fact, but in the purpose and promise of God, Rom 4:17; Abraham has not only been the father of many nations, in a literal sense, as before observed, but in a mystical sense, of the whole world; that is, of all in it that believe, whether Jews or Gentiles; and so the Rabbins (i) interpret it: at first, they say, he was the father of Aram, and therefore his name was called Abram, but now he is the father of the whole world, and therefore called Abraham; and so Maimonides (k) himself says, quoting this passage,"behold he is the father of the whole world, who are gathered under the wings of the Shechinah.'' (g) Smegma Oriental. p. 88. (h), "numerus", "copiosus", Golius, col. 1055, 1056. Castel. col. 3537. (i) In Massechet Biccurim, apud Galat. in Arcan. Cathol. Ver. l. 5, 13. & 9, 12. in Maimon. in Misn. ib. c. 1. sect. 4. (k) Hilchot Biccurim, c. 4. sect. 3.”

“Thy name shall be Abraham - Abram אברם literally signifies a high or exalted father. Ab-ra-ham אברהם differs from the preceding only in one letter; it has ה he before the last radical. Though this may appear very simple and easy, yet the true etymology and meaning of the word are very difficult to be assigned. The reason given for the change made in the patriarch's name is this: For a father of many nations have I made thee, אב המון גוים ab-hamon goyim, "a father of a multitude of nations." This has led some to suppose that אברהם Abraham, is a contraction for אב רב המון ab-rab-hamon, "the father of a great multitude." Aben Ezra says the name is derived from אביר המון abir-hamon, "a powerful multitude." Rabbi Solomon Jarchi defines the name cabalistically, and says that its numeral letters amount to two hundred and forty-eight, which, says he, is the exact number of the bones in the human body. But before the ה he was added, which stands for five, it was five short of this perfection. Rabbi Lipman says the ה he being added as the fourth letter, signifies that the Messiah should come in the fourth millenary of the world. Clarius and others think that the ה he, which is one of the letters of the Tetragrammaton, (or word of four letters, יהוה YeHoVaH), was added for the sake of dignity, God associating the patriarch more nearly to himself, by thus imparting to him a portion of his own name. Having enumerated so many opinions, that of William Alabaster, in his Apparatus to the Revelation, should not be passed by. He most wisely says that ab-ram or ab-rom signifies father of the Romans, and consequently the pope; therefore Abraham was pope the first! This is just as likely as some of the preceding etymologies. From all these learned as well as puerile conjectures we may see the extreme difficulty of ascertaining the true meaning of the word, though the concordance makers, and proper name explainers find no difficulty at all in the case; and pronounce on it as readily and authoritatively as if they had been in the Divine council when it was first imposed. Hottinger, in his Smegma Orientale, supposes the word to be derived from the Arabic root rahama, which signifies to be very numerous. Hence ab raham would signify a copious father or father of a multitude. This makes a very good sense, and agrees well with the context. Either this etymology or that which supposes the inserted ה he to be an abbreviation of the word המן hamon, multitude, is the most likely to be the true one. But this last would require the word to be written, when full, אב רם המון ab-ram-hamon. The same difficulty occurs, Gen 17:15, on the word Sarai, שרי which signifies my prince or princess, and Sarah, שרה where the whole change is made by the substitution of a ה he for a י yod. This latter might be translated princess in general; and while the former seems to point out her government in her own family alone, the latter appears to indicate her government over the nations of which her husband is termed the father or lord; and hence the promise states that she shall be a mother of nations, and that kings of people should spring from her. See Gen 17:15, Gen 17:16. Now as the only change in each name is made by the insertion of a single letter, and that letter the same in both names, I cannot help concluding that some mystery was designed by its insertion; and therefore the opinion of Clarius and some others is not to be disregarded, which supposes that God shows he had conferred a peculiar dignity on both, by adding to their names one of the letters of his own: a name by which his eternal power and Godhead are peculiarly pointed out. From the difficulty of settling the etymology of these two names, on which so much stress seems to be laid in the text, the reader will see with what caution he should receive the lists of explanations of the proper names in the Old and New Testaments, which he so frequently meets with, and which I can pronounce to be in general false or absurd.”

“but thy name shall be Abraham--In Eastern countries a change of name is an advertisement of some new circumstance in the history, rank, or religion of the individual who bears it. The change is made variously, by the old name being entirely dropped for the new, or by conjoining the new with the old; or sometimes only a few letters are inserted, so that the altered form may express the difference in the owner's state or prospects. It is surprising how soon a new name is known and its import spread through the country. In dealing with Abraham and Sarai, God was pleased to adapt His procedure to the ideas and customs of the country and age. Instead of Abram, "a high father," he was to be called Abraham, "father of a multitude of nations" (see Rev 2:17).”