"Not alone for men in positions of large responsibility is the lesson of Elijah's experience in learning anew how to trust God in the hour of trial. He who was Elijah's strength is strong to uphold every struggling child of His, no matter how weak. Of everyone He expects loyalty, and to everyone He grants power according to the need. In his own strength man is strengthless; but in the might of God he may be strong to overcome evil and to help others to overcome. Satan can never gain advantage of him who makes God his defense. “Surely, shall one say, in the Lord have I righteousness and strength.” Isaiah 45:24 . PK 175.1"
"Surely, shall one say, in the Lord have I righteousness and strength: even to him shall men come; and all that are incensed against him shall be ashamed."
EGW directly quotes Isaiah 45:24 and uses it to support her point about God providing strength.
"I can do all things through Christ which strengtheneth me."
Both passages deal with the idea of strength coming from God, but EGW's passage is more directly tied to the Isaiah verse she quotes. Philippians 4:13 is a related theme but not a direct basis.
"I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing."
Both passages convey the idea that believers are conduits or channels of God's power. The John 15:5 passage provides a more detailed analogy of the vine and branches, while EGW's statement is a concise summary of the same principle.
"To us, as to Peter, the word is spoken, “Satan hath desired to have you, that he may sift you as wheat: but I have prayed for thee, that thy faith fail not.” Luke 22:31, 32 . Christ will never abandon those for whom He has died. We may leave Him and be overwhelmed with temptation, but Christ can never turn from one for whom He has paid the ransom of His own life. Could our spiritual vision be quickened, we should see souls bowed under oppression and burdened with grief, pressed as a cart beneath sheaves, and ready to die in discouragement. We should see angels flying quickly to the aid of these tempted ones, forcing back the hosts of evil that encompass them, and placing their feet on the sure foundation. The battles waging between the two armies are as real as those fought by the armies of this world, and on the issue of the spiritual conflict eternal destinies depend. PK 175.3"
"But I have prayed for thee, that thy faith fail not: and when thou art converted, strengthen thy brethren."
EGW directly quotes Luke 22:31-32 and builds upon the idea of Christ's intercession for believers facing temptation.