In 1 Cor 10, the apostle Paul related how the fathers tempted Christ in the wilderness and were destroyed by serpents.
KJV 1 Corinthians 10
Vs. 1 "Moreover, brethren, I would not that ye should be ignorant, how that all our fathers were under the cloud, and all passed through the sea;”
Vs. 5 “But with many of them God was not well pleased: for they were overthrown in the wilderness.”
Vs. 9 “NEITHER LET US TEMPT CHRIST, as some of them also tempted, and were destroyed of serpents."
However, in Heb 3, Paul quotes Psalm 95:7-11 and says, it was the Holy Ghost who spoke (through the psalmist David) "your fathers tempted me...[so] they shall not enter into my rest."
KJV Hebrews 3
7 "Wherefore (as the HOLY GHOST saith, To day if ye will hear his voice,
8 Harden not your hearts, as in the provocation, in the day of temptation in the wilderness:
9 When your fathers tempted ME, proved me, and saw my works forty years.
10 Wherefore I was grieved with that generation, and said, They do alway err in their heart; and they have not known my ways.
11 So I sware in my wrath, They shall not enter into MY REST.)"
So, was it Christ or the Holy Ghost (a separate being according to trinitarian teaching) that they tempted in the wilderness? Or is the Holy Ghost none other than Christ Himself speaking by His Spirit?
Now the Holy Ghost who spoke through the prophets was in fact the Spirit of prophecy, and we are told in Rev 19:10 that "the testimony of Jesus is the Spirit of prophecy." In other words, Jesus inspired the prophets by His Spirit (spirit of prophecy), so that what the prophets wrote is rightly called the testimony of Jesus.
Notice that the Holy Spirit also said "they shall not enter into MY rest." Whose rest are we called to enter into?
Paul went on to warn the Jews against unbelief in Christ in Heb 3:
KJV Hebrews 3
12 "Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God.
13 But exhort one another daily, while it is called To day; lest any of you be hardened through the deceitfulness of sin.
14 For we are made partakers of CHRIST, if we hold the beginning of our confidence stedfast unto the end;
15 While it is said, To day if ye will hear his voice, harden not your hearts, as in the provocation.
18 And to whom sware he that they should not enter into HIS rest, but to them that believed not?
19 So we see that they could not enter in because of unbelief."
Note: If they persisted today in their unbelief, Paul said they would not be able to enter into Christ's rest.
The Jews in Paul's day thought that they had Moses and Joshua who brought their fathers into their promised land and that was the ultimate rest for them. They did not think they needed any other rest that God through Christ was offering them:
“Remember the word which Moses the servant of the Lord commanded you, saying, The Lord your God hath given you REST, and hath given you THIS LAND. …Until the Lord have given your brethren REST, as he hath given you, and they also have possessed THE LAND which the Lord your God giveth them: then ye shall return unto THE LAND of your possession, and enjoy it, which Moses the Lord's servant gave you on this side Jordan toward the sunrising.” (Joshua 1:13, 15)
"So Joshua took the whole LAND, according to all that the Lord said unto Moses; and Joshua gave it for an inheritance unto Israel according to their divisions by their tribes. And THE LAND RESTED from war. (Joshua 11:23)
So Paul said in Heb 4:
4 "For he [Christ by the Holy Ghost] spake in a certain place of the seventh day on this wise, And God did rest the seventh day from all his works.
5 And in this place again, If they shall enter into my rest.
6 Seeing therefore it remaineth that some must enter therein, and they to whom it was first preached entered not in because of unbelief:
7 Again, he limiteth a certain day, saying in David [quoting Psalm 95], To day, after so long a time; as it is said, To day if ye will hear his voice, harden not your hearts.
8 For if Jesus (to be understood as Joshua the son of Nun, which is the Hebrew equivalent of the name Jesus) had given them rest, then would HE (refers to Christ by the Holy Ghost) not afterward have spoken of another day.
9 There remaineth therefore a rest to the people of God.
10 For he that is entered into HIS REST, he also hath ceased from his own works, as God did from his." (bracket mine)
Note that Christ is the antecedent of the pronoun HE (v.4,7,8,10) in Heb 3:6 who spoke by the Holy Ghost through David in Heb 3:7 quoted from Psalm 95.
The first generation of Israelites did not enter into the temporal rest of the earthly Canaan because of unbelief in Christ their invisible leader. A new generation went in under the leadership of Joshua who typified Jesus (in fact they have the same name). But the rest they obtained in the promised land was just temporal, not the ultimate spiritual rest that God had in mind for them, which they could only obtain in Christ Jesus.
So Paul told the Jews, "You think Joshua had given you rest? No, if he had really given you rest--true spiritual rest for your soul, then Christ would not have spoken afterward of another day, which was not the case, because Christ did speak of another day (referring to the day when Christ said by His Spirit through David, Today if you hear His voice, harden not your heart...That you may enter into His rest.)
And when Jesus came into the world physically, He personally extended the invitation to the Jews: KJV Matthew 11 28 "Come unto me, all ye that labour and are heavy laden, and I will give you rest. 29 Take my yoke upon you, and learn of me; for I am meek and lowly in heart: and ye shall find rest unto your souls."
Paul was saying that it was Jesus, the Son of God and not Joshua the son of Nun who could give them true rest for their souls. So if they persisted in their unbelief as did their fathers in the wilderness, they would not enter into the true rest that only Christ could offer.
In conclusion, the Jewish ancestors did not believe and tempted Christ in the wilderness so they died without obtaining the promised rest. Later Christ spoke by His Holy Spirit through David that if they would hear His voice and harden not their hearts and not tempt Him as their fathers did, they would enter into His rest. And now that Christ has come, Paul pointed His readers to the spiritual rest that Christ offered them, and repeated the same warning that Christ has given by His Spirit in Psalm 95. So there remains another rest for God's people, not the temporal rest that Joshua gave them, but the eternal spiritual rest that Christ offers to all His people.
From these Bible texts and inspired statements, we can see how the Holy Ghost is not another being than the Spirit of Christ Himself.