Do not carry the name of the Lord thy God in vain. For the Lord will not hold guiltless” — meaning “will not forgive” — whoever takes His name in vain.
Not hold guiltless does not necessarily mean will not forgive. That appears to be Pragers interpretation of the wording though I do not know if it comes from him or others. Not hold guiltless could also mean that such an action is always sin as opposed to say theft where it is possible that in extreme circumstances (like stealing food to feed a starving child when no other options exist) theft may not be a sin.
There are several places in the Bible that show that God is complex enough that we will never figure Him out entirely. But even if the Bible didn't say it directly, we could still understand this by looking at nature and the fact that God created it in 6 days. We don't even understand the things around us. So how are we going to understand the Creator? Why do I mention this?
Even the love that God has for us is beyond understanding. God sent His Son, Jesus, so that God could hold people guiltless without holding them guiltless. How did He do it? By shifting the guilt onto Jesus, and Jesus, by willingly accepting the guilt, and then the punishment.
In broad and general terms, it's like you lose your job. You can't make your mortgage payments. You are about to lose you house. So, your neighbor pays your mortgage off for you. You couldn't pay then, but even if you get a new and better job, you can't pay on the mortgage any longer. It isn't there. The bank won't accept your payment. You might try paying your neighbor, but even if you can't, the debt is paid.
The point is, you were held guilty in Jesus. And Jesus paid, and then forgave. Jesus was both God and man at the same time. Being God, Jesus could take the pressure of the punishment for all people. Being man, Jesus was a proper one to punish.
This is why it is so important to accept Jesus salvation. Not because you can pay a debt that is already paid. Rather, because if you don't accept Jesus salvation, you are fighting against God. Who will win in that battle?