Heb 1:3
Who being the brightness of his glory, and the express image of his person, and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high;
KJV

"Who being the brightness of his glory"

Jesus Christ, the Son of God is the brightness of His Father's Glory.  Totally obedient to His Father's will, He came here to offer Himself as the propitiation for our sin.  He stood in our place and suffered the punishment we deserved for transgressions He didn't commit. 

"and the express image of his person"

Paul taught the same thing to the Colossian Christians. 

Col 1:15
Who is the image of the invisible God, the firstborn of every creature:

Jesus was the image of God. 

1)    Without sin, (Heb 4:15)
2)    Pure, (1 John 3:3)
3)    Holy, (1 Peter 1:15)
4)    Without spot, (Heb 9:14)
5)    Full of grace and truth, (John 1:14)

"and upholding all things by the word of his power"

We see previously in verse 2 that God created the worlds by Jesus Christ.  We seen now in verse three that Jesus is also the sustainer of "all things."  Nothing is left out.  Everything in the known material universe falls into this category.  The inspired word of God leaves no doubt whatsoever as to the power and authority embodied in the person of Jesus Christ.  

Col 1:16-17
(16) For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him:
(17) And he is before all things, and by him all things consist.

"when he had by himself purged our sins"

Col 1:14
In whom we have redemption through his blood, even the forgiveness of sins:

We learn throughout scripture that the sins of God's chosen people were purged by blood sacrifice.  God's righteous nature demands the punishment of death of all sin, (Rom 6:23).  Adam's sin of disobedience to God required the punishment of spiritual death.  Spiritual death is defined as "everlasting destruction from the presence of the Lord", (2 Thess 1:9).  Throughout history God required the blood of a sacrifice to atone for sin.  Without the shedding of blood there is no remission of sin, (Heb 9:22).  Only the blood of Jesus brings us total forgiveness of our sin.  The atonement of sin God granted because of the animal sacrifices was only a temporary measure.  For it is not possible that the blood of bulls and of goats should take away sins, (Heb 10:4).  The blood of Jesus not only purges our sin, but it also purged the faithful followers of God that lived before the time of Christ on earth. 

Heb 9:15
And for this cause he is the mediator of the new testament, that by means of death, for the redemption of the transgressions that were under the first testament, they which are called might receive the promise of eternal inheritance.

"sat down on the right hand of the Majesty on high"

Heb 10:12
But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God;

The right hand of God.  Similarly, on the Day of the Lord, those who are to receive eternal life are to be placed at the right hand side of Jesus. 

Matt 25:32-34
(32) And before him shall be gathered all nations: and he shall separate them one from another, as a shepherd divideth his sheep from the goats:
(33) And he shall set the sheep on his right hand, but the goats on the left.
(34) Then shall the King say unto them on his right hand, Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world: