What does the Bible say about what it means to be a believer?

According to Scripture, particularly in Ephesians 1:13, there is a distinction between simply believing in Christ and being sealed with the Holy Spirit. Assurance is not the essence of faith; instead, many believers may experience a lack of assurance but still possess genuine faith. This reality is reflected in the experiences and definitions presented in the New Testament, where belief can exist even before a person fully grasps the assurance of that belief. True faith in Christ, even in its infancy, contains the seed of salvation.