"If apostasy arises, and rebellion is manifested, you do not hear them say, in words of encouragement and lofty cheer: Brethren, faint not; be of good courage. “Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are His.” Men who are thus affected by circumstances should remain at their homes and employ their physical and mental strength in a less responsible position where they will not be liable to meet such strong opposition. If everything moves smoothly, they may pass for very good, devotional men. But these are not the ones whom the Master will send to do His work, for this is opposed by those who are emissaries of Satan. Satan also, and his host of evil angels, will be arrayed against them. God has made provision for the men whom He has called to do His work, that they may come off conquerors in every contest. Those who follow His directions will never meet with defeat. 2T 515.1"
"Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his. And, Let every one that nameth the name of Christ depart from iniquity."
EGW directly quotes 2 Timothy 2:19, making it an explicit allusion. The context in EGW's writing further reinforces the meaning of the verse in relation to steadfastness in faith despite apostasy.