Believers receive the Holy Spirit at the moment of salvation, when they place their faith in Jesus Christ (Ephesians 1:13). In the Old Testament, the Spirit would fill certain individuals temporarily for specific tasks (Exodus 31:1-5; Deuteronomy 34:9). In the New Testament, all believers are permanently indwelled (Romans 8:9). The Spirit’s indwelling is distinct from being filled with the Spirit, which can occur multiple times for empowerment or guidance. Scripture confirms that the Holy Spirit seals and marks every believer as God’s own at conversion. Understanding this helps believers recognize that they are never spiritually alone and always have God’s presence within them.
The Holy Spirit is that part of the Trinity that lives inside all believers. When and how He enters our hearts is debated for a couple of reasons. The first is the confusion over the terms "indwelled with the Holy Spirit," "filled with the Holy Spirit," and "baptized by the Holy Spirit." The second reason is the tendency of some to see the receiving of the Holy Spirit in the early church as recorded in the book of Acts as the model for us today.
Today and always, we receive the Holy Spirit the moment we accept Jesus as our Lord and Savior. In John 3:5, Jesus says, "…unless one is born of water and the Spirit, he cannot enter the kingdom of God." When we accept Christ, God immediately seals us with His Spirit (2 Corinthians 1:22).