Wherefore (as the Holy Ghost saith, To day if ye will hear his voice,
etc. Exhortation, from Psalms 95:1-11, not through unbelief to lose share in the spiritual house.
Wherefore - Seeing we are the house of God if we hold fast our confidence, etc. (Hebrews 3:6.) Jesus is "faithful;" be not ye unfaithful (Hebrews 3:5; Hebrews 3:12). The sentence beginning with "Wherefore," interrupted by the parenthetical confirmation from Psalms 95:1-11, is completed at Hebrews 3:12, "Take heed," etc.
Holy Spirit saith - by the inspired Psalmist: the words of the latter are the words of God Himself.
Today - at length: in David's day, as contrasted with the days of Moses in the wilderness, and the whole time since, during which they rebelled against God's voice (Hebrews 3:8). Each fresh time that the psalm is used in public worship, "today" will mean the particular day when used.
Hear - obediently.
His voice - of grace.