Mar 3:28¶ Verily I say unto you, All sins shall be forgiven unto the sons of men, and blasphemies wherewith soever they shall blaspheme:
Alternative: Truly I tell you, All people's mistakes will be gotten rid of, and the false accusations as much as they might blame others [for their own mistakes].
Looking at this in the context of Christ's explanation of his (and our) control over adversity, this statement charts the future progress of each of us as individuals and for human society as a whole. We will let go of our mistakes. We will leave them behind over time. Our foolish actions are not held against us in the future as long as we put them behind us.
The same is true of the way we slander others for our mistakes. Until we let go of our mistakes, it is only natural to blame others, even God, for all the adversity we have in our lives.
All this bad history will be left behind, one way or another. We don't have to keep repeating our mistakes. We don't have to keep dwelling on our past errors. God doesn't dwell on our past mistakes so neither should we.
Relating this to the previous verse about how our houses can be spoiled only if our strengths are first bound, we have authority over our own minds. Making mistakes and bad choices is inevitable and unavoidable. Accusing and blaming others, even God, for what goes wrong in our lives because of that is also inevitable. However, as long as our minds are not enslaved to our inner demons, we will get past these mistakes.
In a larger sense, being enslaved to our inner demons means not letting go of our past errors. Being possessed by evil spirits is being controlled by our bad habits, our worst thoughts, our worst deeds. It means being consumed by blaming others for what we have brought on ourselves. As long as we cannot let go of those deeds, as long as we continue to blame others, we are bound by our inner demons. God can free us but only if we accept that freedom and move on will we let go of our past errors.
"Sins" is from hamartêma (hamartema), which means "failure", "fault," and a "sinful deed." It is midway in meaning between adikêma, which means a "wrong done" or a "wrong" and atuchêma, which means a "misfortune" or "mishap."
"Forgiven" is from aphiêmi (aphiemi), which means "to let fall", "to send away", "to let loose", "to get rid of", "to leave alone", "to pass by", "to permit," and "to send forth from oneself." This is the same word that is translated as "leave" and "forgive" in the New Testament.
"Blasphemies" is from blasphêmia (blasphemia), which means a "word of evil omen", "profane speech", "slander", "defamation," and "abuse." In reading the NT, it came to mean "irreverent speech against God," but this is not what it meant when the Gospels were written.
"Soever" is from the particle an with no real English equivalent, which indicates that something could occur in the future. Closest idea might be something like "perchance."
"Blaspheme" is from blasphêmeô (blasphemeo), which means "to speak profanely of sacred things", "to offer rash prayers", "to speak ill of", "to slander," and, since the NT, "to speak irreverently of God."