Vayeshev תרל”ג 1

תולדות יעקב יוסף.
“These are the children of Yaakov – Yosef” (Bereishis 37:2)
דכתיב בית יעקב אש כו’ יוסף להבה כו’.
This is because Yaakov was the fire however Yosef was the flame that gave the fire it’s strength as it says “The House of Yaakov shall be fire, And the House of Yosef flame” (Ovadia 1:18).
יעקב הוא התורה כה דברי כאש והוא למעלה מהטבע.
Yaakov is compared to the Torah as it says “My word is like fire” (Yirmiya 23:29) which is above nature. (The Torah is what created nature).
רק העצה להיות נכנס אור התורה בנפש האדם. הוא על ידי החשק והתלהבות.
However the way to get the light of the Torah to penetrate into the soul of a person is through desire and excitement.
והוא בחי’ יוסף הצדיק.
This is the idea of Yosef the tzadik.
וז”ש רש”י ע”י להבה שולט למרחוק. כי מצד החשק. מה שאדם מרוחק יותר נתרבה החשק לו להתקרב.
This is what Rashi is refering to “a fire without a flame does not reach far” Because when it comes to desire, the more a person is distanced from that thing the more desire he has for it to become close to it.
וז”ש תולדות יעקב יוסף שע”י חשק הנ”ל נמשך תולדות מבחינות יעקב כנ”ל:
This therefore is the meaning why only Yosef is mentioned as the child of Yaakov, because it is due to the desire that Yosef brings about that the ‘children’ of Yaakov come about. As above.