'Be Strong' in the Bible

The fourth kingdom shall be strong as iron, because iron breaks in pieces and subdues all things; and as iron that crushes all these, shall it break in pieces and crush.

And he said, "Greatly loved man, do not be afraid, peace be to you; be strong, be strong." When he spoke to me, I was strengthened, and said, "Let my lord speak, for you have strengthened me."

And those who act wickedly toward the covenant he shall corrupt by smooth words; but the people who know their God shall be strong, and take action.