By this we know that we abide in Him and He in us, because He has given us of His Spirit.1 John 4:13(NASB)
The privilege and blessing of being indwelt by the Holy Spirit of God is beyond our comprehension, and yet God has given US the permanently indwelling Spirit as PROOF that we live in Him and He in us. And God has recorded this incredible gift of grace to us who believe on the Lord Jesus Christ, in His WORD.
In the Old Testament under the old covenant, the Holy Spirit would come upon certain people to empower them for a particular ministry for which they were chosen, or for a special office to which they had been called. When the job was done or if the individual grieved or displeased the Lord, the Holy Spirit could withdraw. Indeed, the Presence of God was even seen leaving God's holy Temple in Jerusalem because of the disobedience of His people, Israel.
However, in this Church dispensation, every person who trusts in the Lord Jesus as their Saviour is given this incomparable gift of the permanently indwelling Holy Spirit in their heart, as proof from God Himself that we live in Him and He in us.
No one has seen the invisible God at any time, and yet God the Father sent God the Holy Spirit to live in and work through all those who have chosen to trust in God the Son for salvation, by grace through faith.
May the Church of God, which is the Body of Christ, be a potent witness to a lost world that is drowning in sin. Men may not be able to see the Lord, but they can witness His goodness and receive His love through the called and chosen - and that is you and me.
Heavenly Father, thank You that You have given me the Holy Spirit as a witness that I live in You and You live in me. May You be glorified through me and may many come to know of Your free gift of salvation, by grace through faith. In Jesus' name, AMEN.