Baptism of the Holy Spirit...
At the moment of salvation. Without the work of the Holy Spirit there is no spiritual birth. At the moment that a person trusts in Jesus Christ as Savior the Holy Spirit come to indwell them, regenerate them (make them a new creature in Christ) and baptize them (immerse them into the body of Christ). All of that - indwelling, regenerating, baptizing, faith - happens simultaneously and instantly. That is what we call "getting saved".
Titus 3:5-7
"He saved us through the washing of rebirth and renewal by the Holy Spirit, whom he poured out on us generously through Jesus Christ our Savior, so that, having been justified by his grace, we might become heirs having the hope of eternal life."
I Corinthians 12:13
"For we were all baptized by one Spirit into one bodywhether Jews or Greeks, slave or freeand we were all given the one Spirit to drink."
Romans 8:9
"If anyone does not have the Spirit of Christ, he does not belong to Christ."
The baptism of the Holy Spirit is not an experience; rather, it is a fact. One who has come to Jesus Christ in faith for salvation receives all of the work of the Spirit at that moment. We are then called by God's Word to a life of walking in step with the Spirit (which is obedience to the Word). That is also referred to (in Ephesians 5:18) as being "filled with the Spirit".
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