In this particular passage, a great importance is given to the Holy Spirit. Throughout the Holy Bible, many amazing manifestations were credited to the presence of the Spirit, as the life and power of God. But now, the Holy Spirit is identified as a separate Divine Presence in the Blessed Trinity. While the voice of the Heavenly Father is heard from Heaven, the Holy Spirit descended upon Jesus in bodily form like a dove. When John the Baptist stated that the believers would be baptized with fire, such is associated with sanctification and salvation.
Fire represents a sanctifying action.
At the same time, in Scripture, fire is very often associated with the presence of the Saviour-God. God will sanctify His people as through refining fire so they may be made righteous in His eyes to inherit the eternal salvation of the children of God. So great was the Divine Presence of God in the Father, the Son and the Holy Spirit, that all the people were touched, repented of their sins and were baptized. There was no space left for doubters. The voice of God from Heaven echoes the Heavenly Father's hope and determination to save His people.