A proverb meaning 'strike while the iron is hot' — if something is good or timely, act without hesitation.
セールの今が安い。善は急げで、チケットを買っておいた。
The sale price is low now. I struck while the iron was hot and bought the tickets.
チャンスは二度と来ないかもしれない。善は急げだ。
A chance may not come twice. Better act quickly.
面接の予約が取れたら、善は急げで準備を始めよう。
If you get an interview, prepare at once — strike while the iron is hot.