Not boasting of things without our measure, that is, of other men's labours; but having hope, when your faith is increased, that we shall be enlarged by you according to our rule abundantly, Not boasting of things without our measure - We speak only of the work which God has done by us; for we have never attempted to enter into other men's labors, and we study to convert those regions assigned to us by the Holy Spirit. We enter the course lawfully, and run according to rule. See above.
When your faith is increased - When you receive more of the life and power of godliness, and when you can better spare me to go to other places.
We shall be enlarged by you - Μεγαλυνθηναι probably signifies here to be praised or commended; and the sense would be this; We hope that shortly, on your gaining an increase of true religion, after your long distractions and divisions, you will plainly see that we are the true messengers of God to you, and that in all your intercourse with your neighbors, or foreign parts, you will speak of this Gospel preached by us as a glorious system of saving truth; and that, in consequence, the heathen countries around you will be the better prepared to receive our message; and thus our rule or district will be abundantly extended. This interpretation agrees well with the following verse.