unpardonable sin

God not only woos, He warns. Such a salvation as He offers is not to be spurned: the cost is too enormous and the benefits too great, the terms of acceptance too simple and the alternatives too final and dreadful. To turn down God’s offer of salvation is to commit the ultimate unforgivable sin; it is to “crucify … the Son of God afresh” (Heb. 6:6), it is to do “despite unto the Spirit of grace” (10:26), it is to trample under foot the blood of the covenant, it is to become a fitting candidate for God’s eternal and undiluted wrath.

John Phillips, Exploring Acts: An Expository Commentary, The John Phillips Commentary Series (Kregel Publications; WORDsearch Corp., 2009), Ac 13:40.