"I saw that all should sing with the spirit and with the understanding also. God is not pleased with jargon and discord. Right is always more pleasing to Him than wrong. And the nearer the people of God can approach to correct, harmonious singing, the more is He glorified, the church benefited, and unbelievers favorably affected. 1T 146.1"
"What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also."
The EGW passage directly echoes the wording of 1 Corinthians 14:15, making it an explicit allusion rather than just a direct principle.
"For God is the King of all the earth: sing ye praises with understanding."
Both passages connect singing praises with understanding. While not a direct quote, the theme is clearly present in both.
"I have been shown the order, the perfect order, of heaven, and have been enraptured as I listened to the perfect music there. After coming out of vision, the singing here has sounded very harsh and discordant. I have seen companies of angels, who stood in a hollow square, everyone having a harp of gold. At the end of the harp was an instrument to turn to set the harp or change the tunes. Their fingers did not sweep over the strings carelessly, but they touched different strings to produce different sounds. There is one angel who always leads, who first touches the harp and strikes the note, then all join in the rich, perfect music of heaven. It cannot be described. It is melody, heavenly, divine, while from every countenance beams the image of Jesus, shining with glory unspeakable. 1T 146.2"
"And when he had taken the book, the four beasts and four and twenty elders fell down before the Lamb, having every one of them harps, and golden vials full of odours, which are the prayers of saints."
Both passages describe harps in heaven and angelic music. EGW provides a more detailed description of the music and the angels playing, but the core imagery is shared.