Walking through the first part of Hebrews
1:1 begins with "God spoke to our fathers by the prophets,"
1:2 declares now God "has spoken to us by his Son, whom he appointed the heir of all things,"
1:3-4 makes both a statement of Christ's nature and work that equates the Son with God, but also as the most exalted of creation as man (v.4)
1:5-14 then quotes a series of OT passages, many from the Psalms, showing why Christ is the greatest of creation.
2:1 warns the reader to pay heed to what is heard; i.e. heard from God, but specifically...
2:2 the law and judgment is "the message declared by angels," while
2:3a salvation "was declared at first by the Lord," and then
2:3b "by those who heard" the Lord, through whom also
2:4 "God also bore witness by signs and wonders and various miracles and by gifts of the Holy Spirit" in those "who heard" the Lord
2:5-18 Discuss mankind's elevation, through Christ's incarnation, work (especially for mankind's salvation), and exaltation.
3:1 asks the reader to consider Christ Jesus as "apostle and high priest" (i.e. His work)
3:2a refers back to "him [God] who appointed him [Christ]," referring back to 1:3 and 2:7-9, but also forward...
3:3b-6 as Christ is shown to be greater than Moses
3:7a explicitly attributes the following quotation of v.7b-11 to Psalm 95:7-11 as "the Holy Spirit says."
3:7b-11 In context the quotation is used to urge the reader to hear God's voice about Christ, using the illustration of what happened to those that did not heed His voice before (Ps 95:7-11 is reflecting back to the people spoken to by God through Moses, Ps 95:7a specifically notes "God" is "his voice" to be heeded in 95:7b).
3:12-14 warns against having the unbelief characterized in v.7b-11; to belong to the house of God through Moses, he needed to be heeded; to belong to the house of God through Christ, He needs to be heeded.
3:15 reiterates the Spirit's statement from Ps 95:11 quoted in 3:11 here.
3:16-19 continues to use Israel in the Exodus as an example of those who failed to believe, and thus failed to enter and find rest.
4:1-2 warns that one now reading can fail to enter into rest because of unbelief; one just needs to believe "the good news" that came to enter (4:3a).
4:3a The "he has said" begins some ambiguity, as it could be either the Spirit specifically (so 3:7, 11) or God generically (so Ps 95:7), given that this only quotes Ps 95:11, which is an explicit statement of God's about a yet prior statement.
4:3b The message is still those who believe enter the rest, even though the rest of God began long ago (v.3b)
4:4a "he has somewhere spoken," continues to carry the same ambiguity from 4:3a, as the quotation of 4:4b is to Gen 2:2 (or possibly Exo 20:11 or 31:17)
4:5 "he said" again ambiguous, still referencing the direct quote from God of Ps 95:11.
4:6 Some still need to enter rest by receiving the good news (i.e. believing)
4:7a So "today" has been appointed as the time for that to happen. It is "He" who appointed the day that is also "saying through David," and then references
4:7b the first part of the quote given in Hebrews 3:7b-8a (and 3:15), which is Ps 95:7b-8a, and is the writing of David to heed God's voice (Ps 95:7a), who David is speaking on behalf of through a first person reference in Ps 95:9-11 (as a "prophet," so Hebrews 1:1).
Hebrews 1:1 and 3:7, along with the context of Ps 95, seem to hold the key to answering the "He" of Hebrews 4:7.
It is God speaking through David as a prophet (so Heb 1:1; via writing of Ps 95:7-11) by the agency of the Holy Spirit speaking the message from God (so Heb 3:7) through David (so Heb 4:7).
But the quote given in Heb 4:7 is that part of the quote where David is still speaking as a person apart from God, to "hear his voice," before transitioning to the direct statements of God that follow in the first person. Yet Heb 3:7 attributes this first part as well to the Spirit speaking, and so it is directly the Spirit that speaks through David (in Heb 4:7).
But the Spirit is also who speaks through David for the first person references, and so it is God as Spirit (i.e. the Spirit is part of the Godhead) that is speaking the entirety of the Ps 95:7-11 reference, and the "me" references of the Psalm thus point back to the Godhead through association with the Spirit that is speaking through David. Thus, what appears to be ambiguity in 4:3-5 really is not, as the Spirit is as much God as not, and other Scripture shows that Scripture itself is a product of the Spirit.
In short, the combination of references of Heb 1:1, 3:7, 4:7 and Ps 95:7-11 appear to affirm both
- The Spirit's inclusion as being God (just as 1:3-4 was including the Son as God), for He was speaking in Ps 95 in the me statements.
- The Spirit's work of inspiration of the text of Psalm 95 through David.