1 Corinthians 12:13 explains that by the baptism of the Spirit believers are added to the church, the body of Christ.
“For by one Spirit we were all baptized into one body—whether Jews or Greeks, whether slaves or free—and have all been made to drink into one Spirit.” [1]
Acts 11:15-16 explains the words of the Lord Jesus in Acts 1:5 regarding this baptism, that He meant the day of Pentecost when the Spirit came upon the company of believers.
“And as I began to speak, the Holy Spirit fell upon them, as upon us at the beginning. Then I remembered the word of the Lord, how He said, ‘John indeed baptized with water, but you shall be baptized with the Holy Spirit.’” [1]
This, combined with the passage in 1 Corinthians, makes clear that the body of Christ, the church, did not come into existence until the day of Pentecost, which automatically excludes the nation of Israel from the Old Testament being part thereof. The baptism of the Holy Spirit happened on the day of Pentecost, though each believer now comes into the good of it at the moment of conversion.
In the Old Testament the Spirit would come upon people, but could depart as well. This happened to Saul when the Spirit came upon him in 1 Samuel 10:10:
“then the Spirit of God came upon him, and he prophesied among them.” [1]
The Spirit then departed in 1 Samuel 16:14:
“But the Spirit of the LORD departed from Saul” [1]
This is why David could cry to the Lord in Psalm 51:11:
“And do not take Your Holy Spirit from me.” [1]
In the current time the Spirit indwells believers permanently. Ephesians 1:13-14 explains that the Spirit is a guarantee of the inheritance of the saints.
“In Him you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also, having believed, you were sealed with the Holy Spirit of promise, who is the guarantee of our inheritance until the redemption of the purchased possession, to the praise of His glory.” [1]
Therefore, to lose the Spirit would be to lose salvation. A person at this time cannot be saved without the Holy Spirit indwelling him or her. The words of Paul in Romans 8:38-39 indicate that there is nothing in all creation that can separate a believer from the love of God. That would include the believer in question.
“For I am persuaded that neither death nor life, nor angels nor principalities nor powers, nor things present nor things to come, nor height nor depth, nor any other created thing, shall be able to separate us from the love of God which is in Christ Jesus our Lord.” [1]
Every believer, since the day of Pentecost, is indwelled by the Holy Spirit as part of the body of Christ, the church. This differs completely from those of Israel and previous times when the Spirit didn’t indwell believers.
Would anyone claim that no one in the Old Testament is in heaven? No one in the Old Testament was indwelled by the Holy Spirit and are not part of the church. Israel and the church are distinct. Previously it was shown that God is not done with Israel. Dispensationalism does teach the scriptural truth of a distinction between Israel and the church, and does teach that God is not done with Israel. In this dispensational teaching lines up with scripture.
[1] New King James Version, 1982, Thomas Nelson, Inc.
Thinking About The Truth 