Zeller believed that education was the main method to get to the heart of the people and to increase the Protestant influence in Nazareth and the area.
He also assisted his Armenian colleague Kaloost Vartan of the Edinburgh Medical Missionary Society in the founding of the Nazareth Hospital.
Zeller’s activities contributed significantly to the establishment and the growth of the denomination,[3] especially in Nazareth where the need to build a proper center became a pressing one.
In Jerusalem he took charge of the Bishop's School and founded a Preparandi Institute which was devoted to training teachers.
Zeller left behind him a long list of people (especially indigenous) whom he had trained and equipped properly for the ministry in the Middle East.
[8] During his ministry in Nazareth he helped to establish the Anglican school, the Protestant Church, and an orphanage for girls, thus making a great contribution to the city and the whole Galilee.