Be "on your guard" - Guard your heart and spirit from the enemies influences.
Be "firm in your faith" - It is time to "stand fast" in our most holy faith.
Be "courageous" - Stay courageous in the word of God.
Be "strong" - That your faith should not stand in the wisdom of men, but in the power of God. 1 Corinthians 2:5
Be on your guard; stand firm in the faith; be courageous; be strong. - 1 Corinthians 16:13