John Milton was not a man of inferior learning - unlike many who write Christian books in the modern era. His place in literature is right up there with William Shakespeare. He is considered by many to be the greatest English poet.

He was well read in his own day. No doubt he lost a few friends over these words... as also over his Considerations Touching the Likeliest Means to Remove Hirelings Out of the Church, 1659.

I can see why he was not invited by the Long Parliament to join other Puritans at the Westminster Assembly. Church & State relations then meant that, throughout the British Empire, the general public would be taxed in order to pay the clergy. An idea which he found intolerable.