What is the biggest sin for a Christian?
Eternal sin
eternal sins, unforgivable sins, or unpardonable sins
In Christian hamartiology, eternal sins, unforgivable sins, or unpardonable sins are sins which will not be forgiven by God. One eternal or unforgivable sin (blasphemy against the Holy Spirit) is specified in several passages of the Synoptic Gospels, including , , and .