The answer
There is a difference between using the word Master when we talk about our Lord Jesus Christ for He is the Master of all and when we address others as of respect. In the world today we address men and women by Mr., Mrs., or Miss as a sign of respect to the person. This does not make them by any means masters over us. When we address His Holiness the Pope or the bishops with the word Sayedna we always have in mind that they represent our Lord on this earth.As for the titles 'His Grace' and 'His Holiness', they mean the Grace and the Holiness of God that are bestowed on them not because of their worthiness but because of their office and role in the church. So it is a constant reminder to them of the gift of God that they have received and which they should use for His glory.
Answered by His Eminence Metropolitan Youssef (opens in a new tab)