"God... only forgets when He intends to. This is because His capacity to remember is infinite. He can’t forget anything! That is, of course, unless He means to...
The only thing that God willfully forgets is sin. But how does He actually do that? If His capacity to remember is infinite and infallible, how can He make something disappear from His memory?
He does not magically wish our sins away. Instead, He “remembered” your sins on Christ, and as a result He “remembers” Christ’s righteousness on you! This forgetful act on our behalf is the supreme display of His abundant love. It is incalculably wonderful to consider and to savor."

Dustin Smetona, The Forgetful God