Protestantism:
Scripture is the pillar and ground of truth.

Roman Catholicism:
The Papacy is the pillar and ground of truth.

Eastern Orthodoxy:
"The Church is the pillar and ground of truth." (1 Tim 3:15)

The Church is the whole family, headed by Christ, and when we look at the early Church, they tested against scripture, and they honored the Pope, but they saw the family as the true witness to what was Apostolic.

Popes are fallible and so is our scriptural interpretation, but the living marriage of believers in one body, with one Faith, by one Spirit, is the testimony to what a Christian should cling to.

Some Orthodox, trying to get the same feeling of control that Sola Scriptura and Papal Supremacy bring, try and make the Ecumenical Councils the top of the totem, but we only know which councils are Ecumenical by the testimony of the Church. There were many councils.