The Great Controversy does not contain a direct quote with the exact wording you mentioned, but Ellen G. White addresses the idea that there is more to being a minister than just preaching in several of her books. Here is a representative quote from her writings that captures this concept:
"Ministers, preach the truths that will lead to personal labor for those who are out of Christ. Encourage personal effort in every possible way. Remember that a minister's work does not consist merely in preaching. He is to visit families in their homes, to pray with them, and to open to them the Scriptures. He who does faithful work outside of the pulpit will accomplish tenfold more than he who confines his labors to the desk." (Testimonies for the Church, Vol. 9, p. 124.1)
While this quote is not from The Great Controversy, it clearly expresses the principle that the minister's role involves much more than preaching—it includes personal labor, visiting, praying, and teaching.
If you are looking for a specific passage in The Great Controversy itself, there isn't adequate information in the available sources to provide an exact match to your request. However, the above quote and others from Ellen White's writings affirm the broader responsibilities of ministers beyond preaching.
References:
- White, E. G. (1915). Testimonies for the Church, Vol. 9, p. 124.1.
- White, E. G. The Great Controversy. (No direct match found for your requested wording.)