Rabbi M Ch Luzzatto in Derech HaShem (1:2:1) gives HaShem’s purpose in creation to “bestow of His good to another”. (Translation Aryeh Kaplan.) The translator in his notes gives several sources/references for this which I find very difficult to locate even at Hebrewbooks.com. They are: Emunos VeDeyos 2:1 end, 3:0; Or HaShem (Crescas) 2:6:2; Sefer HaYashar 1; Pardes Rimonim 2:6; Eitz Chayim Shaar HaKelalim %1
How does Ramchal (or any of the references) know that this was HaShem’s purpose?
Is the proof from Tehillim 89(3) כִּי אָמַרְתִּי עוֹלָם חֶסֶד יִבָּנֶה, שָׁמַיִם תָּכִן אֱמוּנָתְךָ בָהֶם?