"God had declared concerning Pharaoh, “I will harden his heart, that he shall not let the people go.” Exodus 4:21 . There was no exercise of supernatural power to harden the heart of the king. God gave to Pharaoh the most striking evidence of divine power, but the monarch stubbornly refused to heed the light. Every display of infinite power rejected by him, rendered him the more determined in his rebellion. The seeds of rebellion that he sowed when he rejected the first miracle, produced their harvest. As he continued to venture on in his own course, going from one degree of stubbornness to another, his heart became more and more hardened, until he was called to look upon the cold, dead faces of the first-born. PP 268.1"
"And the Lord said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go."
Ellen White directly references Exodus 4:21 in this passage.
"places him where a far stronger influence will be ineffectual to make an abiding impression. PP 268.2"
"For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame."
The EGW passage speaks of a point where influence is ineffectual. Hebrews 6:4-6 speaks of a point where repentance is impossible. Both passages speak of a point of no return, though the context is different.
"He who has once yielded to temptation will yield more readily the second time. Every repetition of the sin lessens his power of resistance, blinds his eyes, and stifles conviction. Every seed of indulgence sown will bear fruit. God works no miracle to prevent the harvest. “Whatsoever a man soweth, that shall he also reap.” Galatians 6:7 . He who manifests an infidel hardihood, a stolid indifference to divine truth, is but reaping the harvest of that which he has himself sown. It is thus that multitudes come to listen with stoical indifference to the truths that once stirred their very souls. They sowed neglect and resistance to the truth, and such is the harvest which they reap. PP 268.3"
"Be not deceived; God is not mocked: for whatsoever a man soweth, that shall he also reap."
Ellen White directly references Galatians 6:7 in this passage.