After struggling with the angel Yaakov wanted to know what the angel's name was (Bereishit 32:30):
וַיִּשְׁאַל יַעֲקֹב, וַיֹּאמֶר הַגִּידָה-נָּא שְׁמֶךָ, וַיֹּאמֶר, לָמָּה זֶּה תִּשְׁאַל לִשְׁמִי; וַיְבָרֶךְ אֹתוֹ, שָׁם
And Jacob asked and said, "Now tell me your name," and he said, "Why is it that you ask for my name?" And he blessed him there
The angel doesn't tell him a name because angels' names change (Rashi):
למה זה תשאל: אין לנו שם קבוע, משתנין שמותינו, הכל לפי מצות עבודת השליחות שאנו משתלחים:
Why is it that you ask: (Gen. Rabbah 78:4) We have no permanent name. Our names change, (all) according to the service we are commanded [to do] in the mission upon which we are sent
What is the reason that Yaakov wanted to know the angel's name in the first place and what would Yaakov have gained in knowing it? The angel's answer is strange; by the angel's logic should no angel have a name? Although angels may not have a permanent name couldn't Yaakov have been asking the angel for his current name (i.e. concerning his current mission) and if so why did the angel not reveal the name? This implies that Yaakov was enquiring for the angels fixed name, which he didn't have. If so, why did Yaakov think that the angel had a permanent name?!