"In Prayer I am pained as I see how little the gift of speech is appreciated. In reading the Bible, in engaging in prayer, in bearing testimony in meeting, how necessary is clear, distinct utterance! And how much is lost in family worship when the one offering prayer bows the face down and speaks in a low, feeble voice! But as soon as family worship is over, those who could not speak loud enough to be heard in prayer, can usually speak in clear, distinct tones, and there is no difficulty in hearing what they say. Prayer that is thus uttered is appropriate for the closet, but not edifying in family or public worship; for unless those assembled can hear what is said, they cannot say Amen. Nearly all can speak loud enough to be heard in ordinary conversation, and why should they not speak thus when called upon to bear testimony or to offer prayer? CT 241"
"So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air."
Both passages address the importance of clear and understandable speech, especially in religious contexts. 1 Corinthians 14:9 emphasizes the need for uttering understandable words, while the EGW passage criticizes the lack of clear utterance in prayer and testimony. The EGW passage provides a specific application of the general principle of clear communication.
"When speaking of divine things, why not speak in distinct tones in a manner that will make it manifest that you know whereof you speak, and are not ashamed to show your colors? Why not pray as if you had a conscience void of offense, and could come to the throne of grace in humility, yet with holy boldness, lifting up holy hands without wrath and doubting? Do not bow down and cover up your faces as if there were something that you desired to conceal; but lift up your eyes toward the heavenly sanctuary, where Christ your Mediator stands before the Father to present your prayers, mingled with His own merit and spotless righteousness, as fragrant incense. CT 241.2"
"I will therefore that men pray every where, lifting up holy hands, without wrath and doubting."
The EGW passage directly alludes to 1 Timothy 2:8 by mentioning 'lifting up holy hands, without wrath and doubting' in the context of prayer. The EGW passage expands on this idea by encouraging a confident and open approach to prayer, looking towards the heavenly sanctuary and Christ's intercession.