“See that ye refuse not Him that speaketh. For if they escaped not who refused Him that spake on earth, much more shall not we escape, if we turn away from Him that speaketh from heaven.”- Hebrews 12:25

It does not say, “Refuse not Him that speaketh,” but “See that ye refuse not Him that speaketh”-that is, “be very circumspect that by no means, accidental or otherwise, you do refuse the Christ of God, who now in the gospel speaks to you. Be watchful, be earnest, lest even through inadvertence ye should refuse the prophet of the gospel dispensation-Jesus Christ, the Son of God, who speaks in the gospel from heaven to the sons of men.” It means, “Give earnest heed and careful attention, that by no means, and in no way you refuse Him that speaketh.”…That which Jesus speaks concerns your soul, concerns your everlasting destiny; it is God’s wisdom; God’s way of mercy; God’s plan by which you may be saved. If this were a secondary matter, ye need not be so earnest about receiving it, but of all things under heaven, nothing so concerns you as the gospel. See, then, that ye refuse not this precious Word, more precious than gold or rubies-which alone can save your souls.

Oh! sirs, ye are fallen through your first father, Adam, and the tendencies now of your souls are towards evil, and not towards the right, and when the Lord comes from heaven to you, you will reject Him if left to yourselves. Watch, then, I say; see that ye refuse not, stir up your souls, awaken your minds, lest this delirious tendency of sin should make you angry with your best friend, and constrain you to thrust from you that which is your only hope for the hereafter. When a man knows that he has a bad tendency which may injure him, if he be wise he watches against it. So, knowing this, which God’s Word tells you, watch, I pray you, lest ye refuse Him that speaketh. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/3492.cfm