For I could wish that myself were accursed from Christ for my brethren… – Romans 9:3

Do you know what is the greatest of sins? It is to be at enmity with God! The most damning of iniquities is to refuse Christ! Did God send out of His bosom His only-begotten Son to die for men and do men reject Him? Ah, this is worse than rejecting the Law! This is worse than rejecting the Gospel! It is a direct personal insult to the loving God—this rejecting the Son of God, His only Son, His bleeding, dying Son! Here sin reaches its climax and surpasses itself in infamy! These men rejected Christ and set up their phylacteries, their paying of tithes of anise and mint and cumin, their fasting thrice in the week and I know not what trifles besides, in insulting competition with the Savior! In the same manner at this hour, many persons value their external religiousness above faith in Jesus. They attend to the ceremonies of this church or of the other and refuse the righteousness of God in Jesus Christ! The greatest of sins lies there!

This grieved the Apostle, that they were mad against Him whom they ought to have loved, and were violent against Him in whom they should have believed, so that they had become a race anathematized from Christ! Paul says he could wish that he himself could stand in their place and take that anathema upon himself which he felt was upon them…Some in these days describe the penalty of sin as though it were a trifle. I beseech you, do not regard it as such! There is no hope of blessing for those who die impenitent anyhow or anywhere! They must depart, depart, depart, and that forever! O my Hearer, I beseech you, do not run the risk of the everlasting wrath of God! May God help you, by His infinite mercy, to feel how terrible a thing it is to be out of Christ, for our God is a consuming fire and it is written, “Beware you that forget God, lest I tear you in pieces and there be none to deliver.” My brother, my sister, it is now or never with you. Seek the Lord while He may be found! Call upon Him while He is near! ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/1425.cfm