Huh?

John 10:14-16

14"I am the good shepherd; I know my sheep and my sheep know me— 15just as the Father knows me and I know the Father—and I lay down my life for the sheep. 16I have other sheep that are not of this sheep pen. I must bring them also. They too will listen to my voice, and there shall be one flock and one shepherd."

Specifically verse 16, I have other sheep that are not of this pen. I don't get it. Who are the other sheep?

I have consulted my commentary (The Macarthur Bible Commentary) and it gives a standard 'gentiles' response, but as I read the above I couldn't help but wonder if the implication of the text is wider than that. Now I know who John was writing for and can see how that may have coloured his Gospel, but I wonder all the same...