Christ came to fulfil the Law, not abolish it. It has been changed, not made redundant. Did Christ not command us and His disciples of many things throughout the Gospel - and did his Apostles not do the same throughout the New Testament, on His authority, informed by His oral tradition communicated to them?
To follow Christ is to be Law-abiding; to submit totally to Him.
So if you follow Christ and submit totally to him, what do you need to submit to earthly masters for? Wouldn't that be counter productive?