The Essence of Dovid Is Being Happy & Sameach B'chelko And Singing

Dovid HaMelech was a big Masmid, and his longest Kapit'el (chapter) in Tehillim (קי"ט) is about learning Torah. Yet, Dovid isn't called the "Masmid"; rather he is called: נְעִים זְמִרוֹת יִשְׂרָאֵל (ש"ב כג א) the sweet singer. Being happy and Sameach B'chelko and singing is the essence of a: יֶשׁ לִי כֹל "I-have-everything" Yid, i.e., Dovid.

At the beginning of Sefer Sh'mos, it says that all the Bnei Yisroel came to Mitzrayim אֵת יַעֲקֹב (שמות א א) which means with Yaakov.

I always wondered, why doesn't it say the normal Lashon עִם יַעֲקֹב? We can suggest that the Torah is being M'ramez that Yaakov is all the Shevotim in one, and when it says that all the Shevotim came, it's just like saying Yaakov came. And indeed, Chazal say that Klal Yisroel are called Yaakov, (for example: לֹא הִבִּיט אָוֶן בְּיַעֲקֹב (בלק כג כא) which means the entire Klal Yisroel).