פלגי - מגזרת פלג לשונם. [Beside] streams (פַּלְגֵי - palgei): From the same root as (Genesis 10:25) "divided" (peleg) [referring to dividing/channeling water].
ועל פלגי מים - על אחת הפלגים, כמו: אל ירכתי הספינה, ויקבר בערי גלעד, בן אתונות. ויש אומרים: כי טעם פריו – כמו בני הנעורים. Beside streams of water (עַֽל־פַּלְגֵי־מָ֥יִם - al palgei mayim): Means beside one of the streams. Similar [constructions where a plural denotes one instance within a category include]: "to the innermost parts (yarketei - plural construct) of the ship" (Jonah 1:5) [referring to one area]; "and he was buried in the cities (be-arei - plural construct) of Gilead" (Judges 12:7) [meaning in one city]; "son of she-asses" (atonot - plural) (Zechariah 9:9) [likely referring to the foal of one specific donkey]. And some say (v'yesh omrim): That the meaning of "its fruit" (piryo) is analogous to "children of youth" (Psalm 127:4) [interpreting the fruit metaphorically as descendants].
ועלהו לא יבול - עשרו כל ימיו על דרך טובה חכמה עם נחלה. Whose foliage never fades (וְעָלֵ֥הוּ לֹֽא־יִבּ֑וֹל - ve-alehu lo yibol): [This represents] his wealth (oshro) enduring all his days, in the sense of (Ecclesiastes 7:11): "Wisdom is good with an inheritance" [implying enduring substance].
וכל אשר יעשה יצליח - ישוב על האדם הנמשל לעץ. ויש אומרים: כי ישוב כל אשר יעשה יצליח - על העץ כי אם יוקח ממנו סעיף ויוטע יצליח. ואחרים אמרו: כי שב על עלהו כמו: ועלהו לתרופה. ולפי דעתי: כי טעם פריו - הנשמה החכמה שתהיה מלאה תורת אלהים להכיר בוראה ומעשיו העומדים לנצח, ותדבק בעולמה העליון בהפרדה מעל גויתה, כמו הפרי המבושל באילן ויפרד ממנו ואין צורך לו, כי בעבור הפרי היה העץ. And whatever it produces thrives (וְכֹ֖ל אֲשֶׁר־יַעֲשֶׂ֣ה יַצְלִֽיחַ - ve-khol asher ya'aseh yatzliach): This refers back to the person (ha-adam) who is compared to the tree. And some say (v'yesh omrim): That the phrase "whatever it produces thrives" refers back to the tree itself – meaning that if a branch (sa'if) is taken from it and planted, it will thrive. And others have said (v'acherim amru): That it refers back to "its foliage" (alehu), similar to (Ezekiel 47:12) "and its foliage shall be for healing" [li-trufah - implying the leaf itself produces a successful outcome]. And according to my opinion (u-lefi da'ati): The meaning of "its fruit" (piryo) is the wise soul (ha-neshamah ha-chakhamah) that will be filled with God's Torah, enabling it to recognize its Creator and His deeds which endure forever. It [the soul] will cleave to its supernal world upon separation from its body, like ripened fruit on a tree that separates from it and no longer needs it – for the tree existed for the sake of the fruit.
ועלהו לא יבול – זכרו הטוב, כדרך זכר צדיק לברכה "Whose foliage never fades" (ve-alehu lo yibol) [represents] his good reputation (zikhro ha-tov), in the manner of (Proverbs 10:7) "The memory of the righteous is a blessing" (zekher tzaddik li-verakhah).
וכל אשר יעשה יצליח - הון ובנים וכבוד. "And whatever it produces thrives" (ve-khol asher ya'aseh yatzliach) [refers to worldly success:] wealth (hon), children (banim), and honor (kavod).