"As many of us as were baptized into Christ Jesus were baptized into His death." (Rom. 6:3)
"Unless you eat the flesh of the Son of Man and drink His blood, you have no life in you." (John 6:53)
The sacraments of the New Testament are baptism and the Lord's Supper. These, and these alone, were instituted by Christ to be part of the ministry of his church (see Matt. 28:19; 1 Cor. 11:26).
The written promises of God are not enough for us. If they were, God would not have instituted sacraments as visible forms of his promises and his work of redemption. So what do they add?
The answer is that sacraments give objective signs and seals of those promises to all those who are entitled to receive them, and to all who receive them in faith. Your personal faith can be a very subjective thing. Sacraments, by their very nature, are objective.
The written promises go to all people who read or hear them. But baptism is given only to those who are entitled to be regarded as part of the Christian church, by profession of faith or by birth into a family with at least one believing parent. The Lord's Supper is given only to those who have demonstrated maturity in the faith (that is, ability to "discern the Lord's body") and commitment to it by making a public profession of faith.
In both sacraments, individuals are given objective things (water; bread and wine) that demonstrate the blessings of Christ promised to them personally. Of course, they must still believe these promises and live out of that faith, but it nevertheless remains that the sacraments given to them are objective evidences of Christ's love for them. And the fact that they are given by a minister of Christ further shows that Christ himself is ministering personally through these objective signs that he has ordained.
Our faith is so often weak, assaulted, and full of unbelief. Sacraments are visible signs and seals of the promises of the new covenant, encouraging us to look, not at our faith, but at Jesus Christ and his objective work in history.
Isn't that the way we are saved from sin and death?