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.
Beloved. Sound doctrine kindles Christian love. Doubters of the resurrection have no motive to zeal in the Lord's work.
Steadfast - not turning aside from the faith of yourselves.
Unmoveable - not turned aside by others (1 Corinthians 15:12; Colossians 1:23).
The work of the Lord - the promotion of Christ's kingdom (Philippians 2:30).
Not in vain - as deniers of the resurrection would make it (1 Corinthians 15:14; 1 Corinthians 15:17).
In the Lord - applying to the whole sentence and its clauses Ye, being in the Lord by faith, know that your labour in the Lord (i:e., according to His will) is not to be without its reward in the Lord (through His merits and according to His gracious appointment).