Ye ought to forgive one another; for he that forgiveth not his brother his trespasses standeth condemned before the Lord; for there remaineth in him the greater sin.”
D&C 64:9 (cf Matthew 6:15; 18:35; et al).
Do you have enough faith to believe Christ?
If you do, then what did he mean?
We are children. We are little children in a mortal life. The only things we truly accomplish in life are the changes we make in ourselves that we take with us into the next life. Of those changes, the core change is to open ourselves to the love of Christ so that we can let charity embrace us.
Others can do us meaningful harm only by our failure to love them, our failure to forgive them, our hardening our hearts away from God. Nothing else is lasting.
The bottom line is that nothing that happens to us in this life can do us any real harm except for those things we do to ourselves. Only the embrace of bitterness and the rejecting of the love of God so that we refuse to forgive, damages us or causes any pain that escapes the grave.