Their heresy is said to be the lack of forgiveness, yet the others did the same thing.
I have a feeling that my admittedly brief reply to Gebre is being misunderstood. Please allow me to clarify. I did not mean that the heresy of the Donatists was not forgiving (in itself, full stop), but that by
not forgiving those who had strayed, and making it a matter of doctrinal strictness (or however you want to put it) that they should not
be forgiven, the Donatists in effect denied the forgiveness inherent in Christ's teachings, life, death, and resurrection, thereby warping Christianity itself into a religion very different than the Orthodox Christian faith that had been entrusted to them (and to all of us). As has been pointed out in this very thread, it is recognized that when giving His apostles the power to forgive sins, our Lord did say that whatsoever sin you forgive shall be forgiven and whatsoever you retain shall be retained. This is well and good, but also a far cry from "Don't forgive anyone should they stray." In fact, we need only meditate upon our Lord's forgiveness of St. Peter who denied Him three times to see in effect what damage the Donatists' and other rigorists' positions do to our religion. I hope you won't respond to this with any kind of reply suggesting that giving up written scriptures should be seen in a worse light than denying the Word of God in the flesh about Whom those scriptures testify.
So as Christ forgave the errant Peter, it would have been right for those calling themselves Christians (whether Donatists or not) to follow His example and forgive those who had erred in their own day. This is what I meant by posting that their error was that they had denied forgiveness. To be strict with people for their benefit in a pastoral setting is one thing; to out-and-out deny the efficacy of forgiveness/reconciliation (as I understand the Donatists did) such that you teach and practice that those who fell away can never be absolved is quite another. Christ's life, death, and resurrection was not for the perfect, of which there are none but Him anyway.
Repentance is not always necessary to forgive, as Christ forgave those who crucified him.
Of course. I would forgive the Donatists of their errors, gladly, that they may be reconciled with the Church from which they split. But reconciliation and reception into the Church
does require a repudiation of errors. Anyone who has been through an Orthodox baptismal service upon being received from another tradition will tell you (if they are old enough to remember, that is) that it involves renunciation of errors. The Donatists and any others would have to do the same. Our Lord forgave those who crucified Him, knowing that they knew not what they were doing. The Donatists, through the years (centuries) of their battles against the Orthodox over this matter during which it was explained to them tirelessly exactly where they had faltered, knew exactly
what they were doing. There is a difference.