serve two masters
To take orders from two superiors or two conflicting parties.
I suspect that Mr Paisley would have been familiar with the biblical quotation: "No man can serve two masters - you cannot serve God and Mammon" (Matthew 6 v 24).
noun
A master's degree.
adj
Of or pertaining to a league or competition limited to players above a certain age or level of experience.
masters meet
noun
A master's degree.
A person holding a master's degree, as a title.