Jamieson, Fausset and Brown on Ephesians 3:2

2. If--The Greek does not imply doubt: "Assuming (what I know to be the fact, namely) that ye have heard," &c. "If, as I presume," The indicative in the Greek shows that no doubt is implied: "Seeing that doubtless," &c. He by this phrase delicately reminds them of their having heard from himself, and probably from others subsequently, the fact. See Introduction, showing that these words do not disprove the address of this Epistle to the Ephesians. Compare Ac 20:17-24.

the dispensation--"The office of dispensing, as a steward, the grace of God which was (not 'is') given me to you-ward," namely, to dispense to you.