If you gain correct ideas on this subject, you will see the necessity of educating and training yourselves so that you may do justice to yourselves, may honor God, and bless others. Put yourselves under patient, efficient teachers, and learn to read in a way that will preserve the melody of the voice. Having an eye single to the glory of God, make the most of the natural capabilities that God has given you, and your intellectual efficiency will increase, and commanding your own powers, you will not become embarrassed by your defects of speech, and your usefulness in the cause of God will be increased. There is need that among our ministers careful attention should be given to the culture of the voice, or many will lie down in untimely graves. The Lord is not glorified by the reflections that are cast upon him, when men attribute to him their sufferings; for the Lord has no pleasure in the suffering and death of his people. He would have them pursue a right course of action, carefully l…
"The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light."
EGW directly references the concept of having an 'eye single to the glory of God' which is the core idea of Matthew 6:22.