Sometimes when a friend admits to feeling guilty, we think we have to make them feel better. People may say, "It's not your fault," or downplay the person's guilt in some other way. But Jay Adams says we actually give hope to people "by taking people seriously when they talk about their sin." Instead of minimizing their self-deprecatory comments, we should try to find out from our friend what they have done that makes them feel guilt.
Of course, the way to deal with guilt is through repentance, forgiveness and reconciliation. Tim Keller has a great article on genuine repentance called All of Life Is Repentance (pdf).
The ultimate solution to guilt is the cross. In his book The Cross-Centered Life, C. J. Mahaney writes:
Here's how to beat condemnation: Confess your sin to God. Then believe in Him. Exercise the gift of faith that God has given you to believe that Jesus died for the very sins you're being condemned for.
The punishment He received was for you. His resurrection is proof that God accepted Jesus' sacrifice. The sins of your past and the sin you just committed were all atoned for; you need carry their weight no more.
You can't do it. That's why Jesus did it for you....
William Law writes, "We may justly condemn ourselves as the greatest sinners we know because we know more of the folly of our own heart than we do of other people's."
So admit you're the worst sinner you know. Admit you're unworthy and deserve to be condemned. But don't stop there! Move on to rejoicing in the Savior who came to save the worst of sinners. Lay down the luggage of condemnation and kneel down in worship at the feet of Him who bore your sins. Cry tears of amazement (pp. 43-44).
What about the guilt we feel for things we didn't do? Some of this "false guilt" is put on us by others. John Piper writes, "There is such a thing as shame that is repeatedly put on people, but which does not belong to them" (Future Grace, p. 139). Other times, we put it on ourselves.
Randy Alcorn says this about combatting false guilt:
Ironically, focus on false guilt can keep us away from facing up to true guilt, which most of us have plenty of. But true guilt can be confessed and dealt with. It should not and need not pile up on us. False guilt is more slippery. No wonder, since Jesus died for our real sins not our imaginary ones.
The only solution to residual guilt is to repeatedly rehearse the facts of forgiveness. Likewise, false guilt is combatted as we rehearse the facts, recognizing that our limitations are not sins.
Remind yourself that God cares for you (1 Peter 5:7), God hears you (Psalm 34: 15), and God understands your limitations and the stress they bring (Hebrews 4: 14-16).
Also, here's something from John Piper on misplaced shame:
How do you battle this misplaced shame? By believing the promises of God that in the end all the efforts to put us to shame will fail. We may struggle now to know what is our shame to bear and what is not. But God has a promise for us in either case:
"Israel is saved by the Lord with everlasting salvation; you shall not be put to shame or confounded to all eternity" (Isaiah 45:17; 49:23).
"No one who believes in the Lord will be put to shame" (Romans 10:11; 9:33).
In other words, for all the evil and deceit judgment and criticism that others may use to heap on us a shame that is not ours to bear, and for all the distress and spiritual warfare it brings, the promise stands sure that they will not succeed in the end. All the children of God will be vindicated. The truth will be known. And no one who banks his hope on the promises of God will be put to shame.