Redemption is about being redeemed. Redemption requires a price be paid for the object being redeemed. Christ redeemed us through the sacrifice of his life. Christ paid the impossible price of redemption. John's message goes beyond redemption to embrace salvation.
Salvation has to do with being made whole.
It has to do with healing the soul's disease of sin. We may be tempted to rush to Christ for redemption without salvation. We may want to be redeemed from sin without accepting God's offer to salvage our lives from sin. We may want redemption, but refuse healing. Our desire to be healed reveals the true nature of our birth.