Torah Temimah points to the teaching that kibbud av va-em is one of the mitzvos whose fruits a person eats in this world while the principal remains for the World to Come (Peah 1:1 / Kiddushin 39b).
English: It was taught: Honoring father and mother is one of the things whose fruits a person eats in this world while the principal remains for him in the World to Come, as it is written concerning it “so that your days may be long and so that it may go well with you.”
On the daf / in context: The double reward language is read as referring to this world (“yiytav lach”) and the next (“ya’arichun yamecha”).
Type of Learning
Diyuk of the double reward clause as this-world fruits and next-world principal.
What Is Learned
Honoring parents yields reward both in this world and in the World to Come; the principal is never exhausted.