The Hebrew calls Naphtali "a hind let loose, that giveth goodly words" (Genesis 49:21). The image is a deer sprinting across a mountainside with news. Targum Pseudo-Jonathan names the specific errand that made the metaphor stick.
"He it was who announced that Joseph was living; he it was who hasteneth to go into Mizraim, and bring the contract of the double field in which Esau had no portion."
Two moments, separated by decades, are folded into one blessing. First, when the brothers returned from Egypt with the shattering news that Joseph was alive and ruling, Jacob's heart fainted (Genesis 45:26). The midrashic tradition (picked up in Bereshit Rabbah 98:17 and Sefer HaYashar) says it was Naphtali who ran ahead and delivered the news — the swift-footed son who could reach his father first.
Second, when Esau later contested Jacob's right to the Cave of Machpelah, Naphtali raced down to Egypt to retrieve the deed — the legal document proving Esau had sold his share of the ancestral tomb. The Targum continues: "When he shall open his mouth in the congregation of Israel to give praise, he shall be the chosen of all tongues." Naphtali the runner became Naphtali the singer — a tribe of beautiful speech, from deed-carrier to poet.