James 1:4 (ESV) … “And let steadfastness have its full effect, that you may be perfect and complete, lacking in nothing.”
But let patience or steadfastness have her perfect work. Let it be fairly developed; let it produce its appropriate effects without being hindered. Let it not be obstructed in its fair influence on the soul by murmurings, complaining, or rebellion. Patience under trials is fitted to produce important effects on the soul, and we are not to hinder them in any manner by a perverse spirit, or by opposition to the will of God. Everyone who is afflicted should desire that the fair effects of affliction should be produced on his mind, or that there should be produced in his soul precisely the results which his trials are adapted to accomplish.
That you may be perfect and entire. The meaning of this is explained in the following phrase— ‘wanting nothing;’ that is, that there may be nothing lacking to complete your character. There may be the elements of a good character; there may be sound principles, but those principles may not be fully carried out so as to show what they are. Afflictions, perhaps more than anything else, will do this, and we should therefore allow them to do all that they are adapted to do in developing what is good in us. The idea here is, that it is desirable not only to have the elements or principles of piety in the soul, but to have them fairly carried out, so as to show what is their real tendency and value.
Wanting or lacking nothing. ‘Being left in nothing;’ that is, everything being complete, or fully carried out.[1]
[1] Barnes, A. (1884–1885). Notes on the New Testament: James to Jude. (R. Frew, Ed.) (pp. 17–18). London: Blackie & Son.