Forgiveness of sins would be followed by the gift of the Holy Ghost, according to Acts 2:3838Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. (Acts 2:38). Such came to pass in Acts 10:4343To him give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins. (Acts 10:43) and 44. The moment the words "remission of sins" passed Peter's lips, the Holy Ghost fell on those who heard. Acts 11:1717Forasmuch then as God gave them the like gift as he did unto us, who believed on the Lord Jesus Christ; what was I, that I could withstand God? (Acts 11:17) shows that it was the gift of the Holy Ghost, in contradistinction to the gifts or signs which then frequently accompanied it. He was given to believers—not to sinners to make them believers; "Forasmuch then as God gave them the like gift as He did unto us, who believed on the Lord Jesus Christ," etc.
I am sure that if I have received remission of my sins by believing in Christ, I have, as a consequence, received the Holy Ghost. This being so, I need no further experience to know that I am united to Christ; for it is the Holy Ghost dwelling in me who effects this. The experience will follow the consciousness of relationship, and will be enjoyed in the cultivation of the things suited to it.
Put the thickness of a gold leaf between the body and the head, and it is a corpse; and such is the union with Christ and His Church, that it is as real as that subsisting between the human body and its head! This union is by the Spirit of God. He unites living members in one body to Christ.