Basically, redemption is collective, while salvation is individual. Christ redeemed humanity collectively from slavery to sin and from the debt of punishment that mankind, as a whole, owed due to sin. Every person, Christian or non-Christian, is redeemed because he is a member of the human race. Salvation is the application of redemption to individuals. A person can choose to reject the graces won for him by Christ even though he has been redeemed.