Be not deceived; God is not mocked: for whatsoever a man soweth, that shall he also reap. Be not deceived - Neither deceive yourselves, nor permit yourselves to be deceived by others. He seems to refer to the Judaizing teachers.
God is not mocked - Ye cannot deceive him, and he will not permit you to mock him with pretended instead of real services.
Whatsoever a man soweth - Whatsoever kind of grain a man sows in his field, of that shall he reap; for no other species of grain can proceed from that which is sown. Darnel will not produce wheat, nor wheat, darnel.