"The Training of Missionaries It is important that we should have intermediate schools and academies. To us has been committed a great work—the work of proclaiming the third angel's message to every nation, kindred, tongue, and people. We have but few missionaries. From home and abroad are coming many urgent calls for workers. Young men and women, the middle-aged, and in fact all who are able to engage in the Master's service, should be putting their minds to the stretch in an effort to prepare to meet these calls. From the light God has given me, I know that we do not use the faculties of the mind half as diligently as we should in an effort to fit ourselves for greater usefulness. If we consecrate mind and body to God's service, obeying His law, He will give us sanctified moral power for every undertaking. CT 209"
"And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people,"
EGW explicitly mentions the 'third angel's message' and the need to proclaim it to 'every nation, kindred, tongue, and people,' which is a direct reference to Revelation 14:6 and its broader context.