What I’m about to tell you is true.
What you lock on earth will be locked in heaven.
What you unlock on earth will be unlocked in heaven.
(Matthew 18:18)

In context of Matthew 18 it does mention forgiveness, but it also mentions faith to ask for anything and then get this anything. This is also said in Matthew 16, in context of Jesus saying He will build His church with Peter’s declaration that He is the Son of God, and this expansion of His kingdom will be so unstoppable that the gates of hell will not prevail against it. Thus, the context allows for a broad use of this. It is an all encompassing power that belongs to followers of Jesus who have faith; this is the same faith one uses to be saved, to be healed, to move mountains, to expand His kingdom, to forgive, and ask for anything you desire. Think about it: you have faith to receive a miracle of wealth, and then use this to fund the gospel mission. Not only did you unlock a financial door here on earth, but by sowing this back into God’s work you have unlocked treasure for yourself in heaven. Faith opens doors on earth, in heaven and in other dimensions. Faith is the master key. Jesus says give to Caesar what belongs to “him.” He says if you tell this mountain to be cast into the sea with faith, it will obey “you,” and etc. Thus, “you” cast out demons and “you” free an enslaved soul who receives Jesus, then what “you” loosed on earth will also be loosed in the next life.