Redemption means that God purchases us with the blood of His own Son from the slave market of sin, self and Satan. But instead of making us His slaves, in love, He makes us His sons.
The idea here is someone loving a person in bondage and slavery so much that they say, “I’ll pay the price to purchase him, no matter the cost.” And so the redeemer becomes the rightful owner of the slave. But instead of making the slave his own slave, he makes him his son. He adopts the slave into his own family, loves him as a son and gives him the full rights of sonship.