"The lack of firmness and self-denial in your characters is a serious drawback in obtaining a genuine religious experience that will not be sliding sand. Firmness and integrity of purpose should be cultivated. These qualities are positively necessary to a successful Christian life. If you have integrity of soul you will not be swayed from the right. No motive will be sufficient to move you from the straight line of duty; you will be loyal and true to God. The pleadings of affection and love, the yearnings of friendship, will not move you to turn aside from truth and duty; you will not sacrifice duty to inclination. 3T 44.1"
"Therefore whosoever heareth these sayings of mine, and doeth them, I will liken him unto a wise man, which built his house upon a rock:"
Both passages emphasize the importance of a solid foundation (firmness, integrity) for a successful spiritual life. The Matthew verse uses the metaphor of a house built on a rock, while EGW speaks of firmness and integrity. The connection is thematic, not a direct quote or allusion.