כִּ֣י אֶת־רַגְלִ֥ים ׀ רַ֙צְתָּה֙ וַיַּלְא֔וּךָ וְאֵ֥יךְ תְּתַֽחֲרֶ֖ה אֶת־הַסּוּסִ֑ים וּבְאֶ֤רֶץ שָׁלוֹם֙ אַתָּ֣ה בוֹטֵ֔חַ וְאֵ֥יךְ תַּעֲשֶׂ֖ה בִּגְא֥וֹן הַיַּרְדֵּֽן׃
’If thou hast run with the footmen, and they have wearied thee, then how canst thou contend with horses? And though in a land of peace thou art secure, yet how wilt thou do in the thickets of the Jordan?
Read kabbalistic (mystical) interpretation of Jeremiah 12:5: and classical mystical sources.