Jamieson, Fausset and Brown on 2 Corinthians 10:15

15. "Not boasting to unmeasured bounds (that is, not exceeding our own bounds by boasting) of (literally, 'in') other men's labors."

when--"As your faith goes on increasing." The cause of his not yet reaching with the Gospel the regions beyond Corinth, was the weakness as yet of their faith. He desired not to leave the Corinthians before the proper time, and yet not to put off preaching to others too long.

enlarged by you--Greek, "in your case." Our success in your case will give us an important step towards further progress beyond you (2Co 10:16).

according to our rule--according to our divinely assigned apportionment of the area or sphere of our work; for "we stretch not ourselves beyond our measure" (2Co 10:14).

abundantly--Greek, "unto exceeding abundance": so as to exceed the limits we have yet reached (2Co 10:16).