Jamieson, Fausset and Brown on 1 Timothy 4:10

10. therefore--Greek, "with a view to this." The reason why "we both ('both' is omitted in the oldest manuscripts) labor (endure hardship) and suffer reproach (some oldest manuscripts read 'strive') is because we have rested, and do rest our hope, on the living (and therefore, life-giving, 1Ti 4:8) God."

Saviour--even in this life (1Ti 4:8).

specially of those that believe--Their "labor and reproach" are not inconsistent with their having from the living God, their Saviour, even the present life (Mr 10:30, "a hundred fold now in this time ... with persecutions"), much more the life to come. If God is in a sense "Saviour" of unbelievers (1Ti 2:4, that is, is willing to be so everlastingly, and is temporally here their Preserver and Benefactor), much more of believers. He is the Saviour of all men potentially (1Ti 1:15); of believers alone effectually.