How do we know Holy Spirit baptism is essential?

The New Testament consistently presents Holy Spirit baptism as the definitive act that brings believers into communion with Christ, granting them remission of sins. Unlike water baptism, which serves merely as an outward sign, Holy Spirit baptism transforms the believer's inner being and provides the foundational assurance of salvation. This doctrine is rooted in passages such as Acts 2:38-39, which convey that the promise of salvation, signified through the Holy Spirit, extends to all who believe.