Biblical explanation
The clearest example is the thief who was crucified beside Jesus. The man acknowledged his guilt, recognized Jesus as the Messiah, and asked Jesus to remember him. Jesus responded with a promise of salvation (Luke 23:39-43). The thief had no realistic opportunity to receive Christian baptism before his death. Another important example is Cornelius. He and his household received the Holy Spirit before Peter baptized them (Acts 10:44-48). Baptism followed God's acceptance of them rather than functioning as a prerequisite that earned that acceptance. Nevertheless, baptism is not optional for a believer simply because salvation is by grace. Jesus commanded baptism (Matthew 28:19-20), and the early believers consistently practiced it. The biblical distinction is therefore important: Baptism does not earn salvation, but a person who has accepted Christ should willingly obey Christ's command to be baptized.
Key takeaway
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.