Belief and baptism work together rather than competing for importance. Jesus Himself was baptized to fulfill righteousness, and He commanded His followers to baptize disciples as part of making them. Paul describes baptism by immersion as a picture of the gospel itself: going under the water pictures being buried with Christ, and coming up pictures rising to a new life empowered by the Spirit. It is a public, obedient response to faith already at work in the heart, not a private feeling kept to oneself, and it marks the believer's identity as belonging to Christ.
Salvation is entirely by grace through faith in Christ. His atoning sacrifice, heavenly ministry, and intercession are the foundation of assurance; obedience, Sabbath faithfulness, and loving service are the fruit of a redeemed life, never a way to purchase acceptance with God.