The Keys are used publicly in the Service of Preparation, but they are also used in private Confession & Absolution. Here a Christian meets with their pastor to confess whatever sin is troubling them. Pastors are bound by their vows not to break the Confessional Seal. What is confessed, stays between the person, pastor, and God.
Even though the regular use of private Confessions and Absolution has fallen into disuse in many congregations, it can be requested where there is no scheduled time for private Confession & Absolution. There are pastors and congregations trying to restore the practice. The beauty of Keys is God speaking directly to you His Absolution through the pastor.
In those moments of spiritual struggle with the Devil and our Flesh, when torment over past sins or doubt of our salvation overcome us, here is a special gift from the Lord forgiving us, and assuring us of His love.