If you engage in this work of mercy and love, will the work prove too hard for you? Will you fail and be crushed under the burden, and your family be deprived of your assistance and influence? Oh, no; God has carefully removed all doubts upon this question, by a pledge to you on condition of your obedience. This promise covers all that the most exacting, the most hesitating, could crave. “Then shall thy light break forth as the morning, and thine health shall spring forth speedily.” Only believe that He is faithful that hath promised. God can renew the physical strength. And more, He says He will do it. And the promise does not end here. “Thy righteousness shall go before thee; the glory of the Lord shall be thy rearward.” God will build a fortification around thee. The promise does not stop even here. “Then shalt thou call, and the Lord shall answer; thou shalt cry, and He shall say, Here I am.” If ye put down oppression and remove the speaking of vanity, if ye draw out your soul to t…
"Let us hold fast the profession of our faith without wavering; (for he is faithful that promised;)"
EGW quotes "He is faithful that promised" directly from Hebrews 10:23 and also alludes to Isaiah 58:8, making the connection clear.
Read Isaiah 58 , ye who claim to be children of the light. Especially do you read it again and again who have felt so reluctant to inconvenience yourselves by favoring the needy. You whose hearts and houses are too narrow to make a home for the homeless, read it; you who can see orphans and widows oppressed by the iron hand of poverty and bowed down by hardhearted worldlings, read it. Are you afraid that an influence will be introduced into your family that will cost you more labor, read it. Your fears may be groundless, and a blessing may come, known and realized by you every day. But if otherwise, if extra labor is called for, you can draw upon One who has promised: “Then shall thy light break forth as the morning, and thine health shall spring forth speedily.” The reason why God's people are not more spiritually minded and have not more faith, I have been shown, is because they are narrowed up with selfishness. The prophet is addressing Sabbathkeepers, not sinners, not unbelievers, …
"Cry aloud, spare not, lift up thy voice like a trumpet, and shew my people their transgression, and the house of Jacob their sins."
EGW explicitly instructs the reader to read Isaiah 58, making the connection direct and intentional.