When trouble comes, to our lives or to our nation, what we have hired out of the world isn’t going to help us. Everything that we have bought or put effort into in an attempt to remain safe, healthy, happy, wealthy, etc… those things will be like, as The LORD points out through Jeremiah, “bullocks of the stall:” ready for the slaughter, fat and unable to move; in short, they will be easy prey. The LORD is speaking to Egypt, a typological picture of the world, and “her hired men” representing the helps the world has to offer:
"Also her hired men are in the midst of her like bullocks of the stall; for they also are turned back, and are fled away together: they did not stand, because the day of their calamity was come upon them, and the time of their visitation." [Jer 46:21]
Those things hired out of the world will not help; they are no defense against times of calamity, or, as is mentioned in this verse, times where God punishes a nation. When “destruction…cometh out of the north” as it were, we must have our defense and help in God alone. And that preparation in The LORD must occur before the trouble strikes!
On a more personal level, we cannot expect to remain in sin and not be punished, just like God promises to turn “into Hell” every nation which “forget[s] God” [Psa 9:17]. And if we are relying on a man or a thing to protect us, we are fooling ourselves. Proverbs says it well,
"The horse is prepared against the day of battle: but victory is of the LORD." [Prov 21:31]
Do not hire out of the world, but instead go to Jesus. Do not use something of the world, saying ‘Oh, but it’s only for a short while’ or recount a phrase the world uses for comfort to avoid the conviction of The Holy Spirit. No, we mustn’t hire things to keep us safe or improve our disposition, but ought only to go to Jesus alone for all our needs and for defense. Remember solemnly the warning of The LORD in Isaiah,
"Woe to the rebellious children, saith the LORD, that take counsel, but not of me; and that cover with a covering, but not of my spirit, that they may add sin to sin: That walk to go down into Egypt, and have not asked at my mouth; to strengthen themselves in the strength of Pharaoh, and to trust in the shadow of Egypt! Therefore shall the strength of Pharaoh be your shame, and the trust in the shadow of Egypt your confusion." [Isa 30:1-3]