וְלֹא־יִקָּרֵ֥א ע֛וֹד אֶת־שִׁמְךָ֖ אַבְרָ֑ם וְהָיָ֤ה שִׁמְךָ֙ אַבְרָהָ֔ם כִּ֛י אַב־הֲמ֥וֹן גּוֹיִ֖ם נְתַתִּֽיךָ׃
이제 후로는 네 이름을 아브람이라 하지 아니하고 아브라함이라 하리니 이는 내가 너로 열국의 아비가 되게 함이니라
Rashi
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).
Chizkuni
ולא יקרא עוד את שמך אברם, “henceforth your name will no longer be called Avram;” anyone still referring to Avraham as Avram will be violating a positive commandment. (Talmud, B’rachot 13)[The underlying reason for this may be that by depriving him of his full name, the caller implies that he was still partially a gentile. This is loosely translated by me for the words לפי שנתלוה עמו גיות, used by the author. Ed.] Nechemyah 9,7 where reference to this name change is made, is no contradiction to what is stated in the Talmud, as it also records what has been written here. The Talmud refers to the difference from Yaakov who was given the additional name Israel, without the name Yaakov having been erased. Seeing that he had been a descendant of Avraham and Yitzchok, the name Yaakov never had a connotation of something connected to paganism which had to be erased. Already Yitzchok’s name never required to be changed.