וְאַתָּה֙ תֶּאְזֹ֣ר מָתְנֶ֔יךָ וְקַמְתָּ֙ וְדִבַּרְתָּ֣ אֲלֵיהֶ֔ם אֵ֛ת כָּל־אֲשֶׁ֥ר אָנֹכִ֖י אֲצַוֶּ֑ךָּ אַל־תֵּחַת֙ מִפְּנֵיהֶ֔ם פֶּֽן־אֲחִתְּךָ֖ לִפְנֵיהֶֽם׃
“Tetapi engkau, ikatlah pinggangmu, bangkitlah, dan sampaikanlah kepada mereka segala yang Aku perintahkan kepadamu. Janganlah gentar terhadap mereka, supaya Aku tidak membuat engkau gentar di hadapan mereka.”
Tze'enah Ure'enah
“So you, gird up your loins, etc.” [1:17]. You Jeremiah, strongly gird up your loins, stand up and speak to them everything that I have commanded you. You should have no fear before them. That is to say, do not be afraid and you will believe that I can protect you. However, if you will be afraid, then I will make you fearful.
Rashi
And you shall gird your loins This is an expression of quickening like a man of valor.