4 Let perseverance finish its work so that you may be mature and complete, not lacking anything.

Read James 1:4 Using Other Translations

But let patience have her perfect work, that ye may be perfect and entire, wanting nothing.
And let steadfastness have its full effect, that you may be perfect and complete, lacking in nothing.
So let it grow, for when your endurance is fully developed, you will be perfect and complete, needing nothing.