Therefore, my beloved brothers, be steadfast (constant), immovable, always abounding in the work of the Lord, knowing that in the Lord your labor is not in vain.1 Corinthians 15:58

Webster “constancy” is Fixedness or firmness of mind; persevering resolution; especially, firmness of mind under sufferings, steadiness in attachments, or perseverance in enterprise; stability; fidelity.