To preach the gospel in the regions beyond you, and not to boast in another man's line of things made ready to our hand.
To - i:e., so as to preach ... beyond you (and) not to boast, etc.
In another man's line of things made ready to our hand. Do not connect "line of things," etc.; but 'boast of things,' etc. Arrange, 'Not to boast as to things (already made by the preaching of others) ready to our hand in another man's line' (i:e., within the sphere apportioned by God to another).