"Before giving a discourse, ministers should take time to seek God for wisdom and power. In earlier times the ministers would often go away and pray together, and they would not cease until the Spirit of God responded to their prayers. Then they would return from the place of prayer with their faces lighted up; and when they spoke to the congregation, their words were with power. They reached the hearts of the people because the Spirit that gave them the blessing prepared hearts to receive their message. There is far more being done by the heavenly universe than we realize in preparing the way that souls may be converted. We are to work in harmony with the messengers of heaven. We want more of God; we are not to feel that our talking and sermonizing can do the work. Unless the people are reached through God, they will never be reached. We are to rely wholly upon God, pleading His promise: “Not by might, nor by power, but by My Spirit, saith the Lord of hosts.” Zechariah 4:6 . 6T 50.2"
"Then he answered and spake unto me, saying, This is the word of the Lord unto Zerubbabel, saying, Not by might, nor by power, but by my spirit, saith the Lord of hosts."
Ellen White directly references Zechariah 4:6 in this passage.