The New Testament teaches that when someone is regenerated the Holy Spirit is with him and will remain with him. It also teaches that we can quench the Holy Spirit, we can be filled, and then, apparently, not so filled with the Holy Spirit. So, the presence and power of the Holy Spirit does rise and fall in the Christian life.
The language of “inviting Him in” implies a second blessing, which the New Testament does not teach. We have the Spirit, but sometimes the Spirit is more active in us, and sometimes we’re more responsive to Him. So, we should certainly seek the presence and power of the Holy Spirit by mortifying sin and listening to His Word, but we should know that He’s always with us as Christians.