Why should we obey Christ instead of disobeying Him?
Because of what Christ has already done, common sense obligates believers to obey His wishes rather than be disobedient. This applies to us today just as it did to the Corinthians. Obedience is the reasonable response to His work, while disobedience contradicts that.
Les explains that on the basis of what Christ had already done, and just as applicable to us today as it was to the Corinthians, common sense tells us that we should be obedient to His wishes and not be disobedient. Paul then beseeches the brethren by the name of our Lord Jesus Christ that they all speak the same thing and that there be no divisions among them. The context shows this instruction was needed because the Corinthian assembly had divisions, though they ought to have had the same mind.