...in these last days has spoken to us in His Son, whom He appointed heir of all things...(Hebrews 1:2)
Upon mentioning the Son of God, the author of Hebrews turns to a series of attributes that relate to the Person and work of Jesus. Namely, the Son is He 1) whom God has appointed heir of all things, 2) through whom God made the world, 3) who is the radiance of God's glory and 4) who is the exact representation of God's nature, 5) who upholds all things by the word of His power, 6) who made purification of sins, 7) who sat down at the right hand of the Majesty on high, and 8) who has become better than the angels, having inherited a more excellent name than they (Hebrews 1:2-4). Each of these attributes serves as the foundation for the Christology that the author develops throughout the letter.
In the first of these descriptions of Christ, the author maintains that God has "appointed [Him] heir of all things" (1:2). Superficially, one might mistake this action of "appointing" to indicate a qualitative difference between the Person of the Father and the Person of the Son with regard to divinity. Put another way, if Christ is God, how can He be "appointed" to a position (i.e., "heir of all things") by another? Would He not, by His own divine nature, already be over "all things"? The question brings up a valid concern, but if taken seriously, ignores or dismisses the fulness of biblical revelation with regard to the Person and work of Jesus, and the Person and work of God.
As we will see as we continue in Hebrews, the author of Hebrews and other New Testament writers maintain that they are constant with prior revelation from God in their claim that Christ is divine, in that He not only is from God but is also of the same being and essence (1:3a; see also Colossians 1:15, 19; 2:9; also John 1:1-2, 18, NASB). Accordingly, when we read or declare that Jesus was "appointed" by God to be "heir of all things," we are not diminishing either the nature of God or the nature of Jesus. Rather, we are describing the particular filial relationship that holds between two Persons of the Triune God. The Father, who is not the Son but is God, "appointed" the Son, who is not the Father but is God, "heir of all things" (see inserted picture above).
To properly understand (as fully as we are able) a notion like the Son being "appointed heir of all things," we have to bear in mind the dual nature of Christ who, by His eternal nature is fully God, and, by His own volition is fully human. Christ has been "appointed" heir of all things, in short, so that God may be "all in all" (1 Corinthians 15:28; see also Colossians 3:11). The Incarnate Deity, wholly able to sympathise with fallen humanity in order to serve as our faithful High Priest, has come to redeem and restore all of creation to a right relationship with God that we might enter in to God's holy presence (Hebrews 2:14-18; 4:14-16). So, God the Son humbled and emptied Himself to be made in the likeness of humankind, so that by His work He might be made "heir of all things" (see Philippians 2:5-11). Though co-equal and co-eternal with the Father, the Son chose to subordinate Himself, and as a faithful servant and heir will subject all things to God, so that God might be all in all, with the end that "all will honor the Son even as they honor the Father" (1 Corinthians 15:28; John 5:23).