Salvation is a pure gift. I would like to quote Barclay in one of His statements, "Grace is a gift." Why? When we study the concept of gift in the theme of salvation, the apostle Paul understood it as a favor (Eph 2:8). The greek word Xaris (charis) some text translated it as a "charity" has many emphases. However, when we talk about salvation in its theological aspect we could never find a single verse that would support salvation as a reward. The bible is clear that we are saved by grace (chariti) through faith. I would like also to give emphasis that the term charis should be understood in the light of its context. Yes, not all charis should be translated as grace. But all of them are related to gifts. If you want more insights about gift and grace, you may read this book, Paul and Grace by John Barclay. Aside from that, you may also refer it to the Handbook of SDA Theology.