Hebrews 1:6 calls the Son the firstbegotten. This does not mean the Son was the first being created by God or even that He was created, for this same verse indicates that the "begetting" occurred after the creation of the angels. Certainly, the Son is not "eternally begotten" because verse 5 describes the begetting as occurring at a certain point in time: "Thou art my son, this day have I begotten thee." So, in what sense is the Son the "firstbegotten"?
The term has several meanings. In one sense of the word, the Son was not just the first begotten but also the only begotten (John 3:16). That is to say, the Son is the only person literally conceived by the Holy Ghost (God); the virgin birth made it possible for complete deity and complete humanity to unite in one person. Moreover, the Son is the firstbegotten in the sense that He was planned in the mind of God before anything else. Furthermore, the Son is the firstbegotten in that He was the first to conquer sin and death. He is "the first-begotten of the dead" (Revelation 1:5), "the firstborn among many brethren" (Romans 8:29), and "the firstborn from the dead" (Colossians 1:18). All these verses of Scripture use the same Greek word, prototokos, as in Hebrews 1:6. Christ was the firstfruits of the resurrection since He was the first to be bodily resurrected and given a glorified body (I Corinthians 15:20).
Since Jesus Christ is the head of the church, which is called the "church of [belonging to] the firstborn" (Hebrews 12:23), we can interpret the designation of Christ as "the firstborn [prototokos] of every creature" in Colossians 1:15 to mean the firstborn of the spiritual family of God that is called out of all creation. Through faith in Him we can become sons and daughters of God by the new birth (Romans 8:14-17). Jesus is the author and finisher of our faith (Hebrews 12:2), the captain of our salvation (Hebrews 2:10), the apostle and high priest of our profession (Hebrews 3:1), and our brother (Hebrews 2:11-12). It is in His redemptive role that He can be called the firstbegotten or firstborn among many brethren.
Christ's title as firstborn has significance not only in the sense of first in order but also first in power, authority, and pre-eminence, just as the eldest brother has pre-eminence among his brothers. As applied to Christ, firstborn does not mean He was the first man physically born, but that He is first in power. This is the primary meaning of Colossians 1:15 when it says He is "the firstborn of every creature," as we see from subsequent verses. Verses 16-18 describe Jesus as the creator of all things, the head of all power, and the head of the church. In particular, verse 18 says He is "the firstborn from the dead; that in all things he might have the pre-eminence."