"But it is in the written word that a knowledge of God is most clearly revealed to fallen man. This is the treasure house of the unsearchable riches of Christ. COL 126.1"
"Unto me, who am less than the least of all saints, is this grace given, that I should preach among the Gentiles the unsearchable riches of Christ;"
The EGW passage uses the exact phrase "unsearchable riches of Christ," which is a direct quote from Ephesians 3:8, indicating a clear and intentional connection.