Looking at the verse of Kohelet (Ecclesiastes) 12:13 I found a couple of translations for כי-זה כל-האדם :
How do I need to understand the meaning of this verse: 'ki zeh kol ha'adam'
Looking at the Mepharshim I saw the following:
(Sources from Sefaria.org)
Rashi
ואת מצותיו שמור כי זה כל האדם . כי לדבר הזה נברא כל האדם :
It is for this matter mankind was created
Metzudos David
כי זה כל האדם. רוצה לומר מה שנאמר למעלה מה שיקרה לאדם בחייו ובמותו, זהו המקרה של כל האדם אין נעדר ולכן מאד הזהר במצות המקום ברוך הוא:
Meaning that which was stated above that which will happen to man in his life and death. This is the fate of everyone and there are no exceptions. Therefore be vigilant with the Mitzvos of the Almighty
Hope this is helpful
The Gemara in Shabbos (30b) says:
אמר רב יהודה בריה דרב שמואל בר שילת משמיה דרב בקשו חכמים לגנוז ספר קהלת מפני שדבריו סותרין זה את זה ומפני מה לא גנזוהו מפני שתחילתו דברי תורה וסופו דברי תורה תחילתו דברי תורה דכתיב (קהלת א, ג) מה יתרון לאדם בכל עמלו שיעמול תחת השמש ואמרי דבי ר' ינאי תחת השמש הוא דאין לו קודם שמש יש לו סופו דברי תורה דכתיב (קהלת יב, יג) סוף דבר הכל נשמע את האלהים ירא ואת מצותיו שמור כי זה כל האדם מאי כי זה כל האדם אמר רבי (אליעזר) כל העולם כולו לא נברא אלא בשביל זה ר' אבא בר כהנא אמר שקול זה כנגד כל העולם כולו שמעון בן עזאי אומר ואמרי לה שמעון בן זומא אומר לא נברא כל העולם כולו אלא לצוות לזה
The Sages sought to suppress the book of Ecclesiastes and declare it apocryphal because its statements contradict each other and it is liable to confuse its readers. And why did they not suppress it? Because its beginning consists of matters of Torah and its end consists of matters of Torah. The ostensibly contradictory details are secondary to the essence of the book, which is Torah. The Gemara elaborates: Its beginning consists of matters of Torah, as it is written: “What profit has man of all his labor which he labors under the sun?” (Ecclesiastes 1:3), and the Sages of the school of Rabbi Yannai said: By inference: Under the sun is where man has no profit from his labor; however, before the sun, i.e., when engaged in the study of Torah, which preceded the sun, he does have profit. Its ending consists of matters of Torah, as it is written: “The end of the matter, all having been heard: Fear God, and keep His mitzvot; for this is the whole man” (Ecclesiastes 12:13). With regard to this verse, the Gemara asks: What is the meaning of the phrase: For this is the whole man? Rabbi Eliezer said: The entire world was only created for this person. Rabbi Abba bar Kahana said: This person is equivalent to the entire world. Shimon ben Azzai says and some say that Shimon ben Zoma says: The entire world was only created as companion to this man, so that he will not be alone.
Ecclesiastes [Kohelet] 12:13 (WLC)
סוף דבר הכל נשמע את־האלהים ירא ואת־מצותיו שמור כי־זה כל־האדם׃
(My translation) The end of all things was heard: Fear God, and keep his commandments—for this is the sole end of man.
The issue is how to understand "all of man" in light of "the end of all things." I argue it's quite straightforwardly to be understood in light of the obvious logical progression: 'I heard the purpose of all things in relation to God: to fear Him, and to obey Him in His requirements as His creature—for this is the end of a man, and indeed his sole purpose, his כל.'
One should not ignore that "because all men this" (כי זה כל האדם) is assumed to logically follow (כי) "the end [read: purpose] of all things is to [worship God]." This more or less necessitates the intepretation: For this is the sole end of man [i.e. as 'the end of all things is to worship God' implies].
