Cheap grace is the preaching of forgiveness without requiring repentance . . .
The exception proves the rule.
We have rules and we have exceptions—each has its proper place.
Today, however, when the topic is forgiveness, we hear many Christians thoughtlessly citing the exception just as if it were the rule; it appears as if they have never heard and applied the true rule. (Shades of Murphy’s Law! See Introduction) We hear the exception from Jesus on the cross (an exceptional circumstance indeed!) with reference to his executioners: “Father, forgive them, for they know not what they do” (Luke 23:34).
When this verse is quoted out of context, the emphasis always falls on “Father, forgive them.” The remainder of the verse is all but forgotten. Who are the “they” who “know not what they do”? I. Howard Marshall explains the verse in this manner: Jesus, addressing God, “asks him to forgive ‘them’ (the executioners, possibly all who are involved in his crucifixion), on the grounds of their ignorance; their sin is unwitting.”*
But Jesus also teaches us the clear rule that forgiveness is conditional based upon the repentance of the sinner: “Take heed to yourselves. If your brother sins, rebuke him; and if he repents, forgive him” (Luke 17:3).
First, note that this concerns a “brother,” that is, a fellow believer.
Here, Jesus’ exhortation to forgive rests upon the conditional phrase, “if he repents.” The International Standard Bible Encyclopedia states, “Jesus recognized that there are conditions to be fulfilled before forgiveness can be granted. Forgiveness is part of a mutual relationship; the other part is the repentance of the offender. God does not forgive without repentance, nor is it required of mankind.”1 (This aspect of a mutual relationship has been banned from today’s self-centered, therapeutic notions about forgiveness.)
In expositing Peter’s preaching on the day of Pentecost (Acts 2:1-47), F. F. Bruce states, “It would be a mistake to link the words ‘for the forgiveness of sins’ with the command ‘be baptized’ to the exclusion of the prior command to repent. . . . blotting out of the people’s sins is a direct consequence of their repenting and turning to God.”
And we must not confuse these two aspects: though forgiveness is conditional on repentance, it is also unlimited, even to seventy times seven.
*The New International Greek Testament Commentary
From Chapter Three, Love, Prayer, And Forgiveness