In the sixteenth and seventeenth centuries, most people believed that a nation could not be politically united unless it had only one church, of which all its people were members. Consequently, the power of the state was generally used to support one church and to suppress all others. "Dissenters" were subjected to various degrees of pressure or restraint to induce them to conform to the established church. Only gradually did dissenters gain liberty of conscience. The intolerance and persecution of which they were the victims meanwhile proved the importance that was attached to the unity of the church, at least within the limits of each nation. This kind of unity without liberty, or compulsory religious unity conceived as an instrument of social control and as essential to political stability, was the expression of a social philosophy which was carried over from medieval Roman Catholic Europe to the modern European nations, both Catholic and Protestant. The idea of unity as an important characteristic of the church did not need to be invented or even discovered in modern times. It was there all the while. But it needed to be liberated from its political entanglements, as the church itself did. It needed to be conceived in terms consistent with the spiritual nature of the church and the civil rights of man. Both the church and the citizen had to be made free.
Besides the efforts of politicians and ecclesiastics in established churches to get church unity by compulsion, there were a few churchmen and independent thinkers who argued that unity might be attained by requiring agreement only upon the few saving essentials of Christianity and leaving everyone free to hold his own opinions on all the doubtful and disputatious matters of doctrine, polity, and ritual. Thus the Puritan Stillingfleet wrote in his _Eirenicon_ (1662):
It would bee strange the Church should require more than Christ himself did, and make other conditions of her communion than our Savior did of Discipleship.... Without all controversie, the main in-let of all the distractions, confusions and divisions of the Christian world hath been by adding other conditions of Church-communion than Christ hath done.