Jamieson, Fausset and Brown on 1 Corinthians 3:8

8. one--essentially in their aim they are one, engaged in one and the same ministry; therefore they ought not to be made by you the occasion of forming separate parties.

and every man--rather "but every man." Though in their service or ministry, they are essentially "one," yet every minister is separately responsible in "his own" work, and "shall receive his own (emphatically repeated) reward, according to his own labor." The reward is something over and above personal salvation (1Co 3:14, 15; 2Jo 8). He shall be rewarded according to, not his success or the amount of work done, but "according to his own labor." It shall be said to him, "Well done, thou good and (not successful, but) faithful servant, enter thou into the joy of thy Lord" (Mt 25:23).