In context, this "wickedness" was the crime of rejecting and influencing others to reject the Lord. While this is not a capital crime in a Christian context, this passage does show how God feels about the sin of unbelief--especially trying to persuade others into unbelief--in the infinite love and sacrifice of Christ who suffered and died for their sins. "He that despised Moses' law died without mercy under two or three witnesses: Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace?" (Hebrews 10:28-29).
Unbelief in Christ is, in fact, the only sin which God cannot forgive, and thus is the most wicked sin of all. Christ died for all our sins, and thus will provide full forgiveness for all who will accept His gift of salvation. Christ Himself said: "He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God" (John 3:18).
One of the final words of the Bible is the warning: "But the fearful, and unbelieving . . . shall have their part in the lake which burneth with fire and brimstone: which is the second death" (Revelation 21:8). These are words spoken by the Lord Jesus, speaking of those who have spurned His sacrificial love. It may seem a light thing in our modern society to ignore or reject Him, but it will eventually prove "a fearful thing" (Hebrews 10:31) to face Him in judgment. HMM