Stand Fast in the Faith
Therefore, my beloved brethren, be ye stedfast, unmoveable, always abounding in the work of the Lord, forasmuch as ye know that your labour is not in vain in the Lord.
- 1 Corinthians 15:58 (KJV)
And...
Watch ye, stand fast in the faith, quit you like men, be strong.
- 1 Corinthians 16:13 (KJV)