“You have come to Mount Zion . . . and to the assembly of the firstborn . . .” (Hebrews 12:22-23, ESV).
The “assembly of the firstborn” is a gathering of people who have been made righteous and perfect by God.
Who was the firstborn in Israel we read about in the Old Testament? It was the oldest male son who was in line to receive the inheritance of the father. So all that the father had accumulated, all the wealth of his kingdom, was inherited by the firstborn. 
And now what do we see here in this passage of Scripture? You and I are the firstborn in the assembly of God. Isn’t this good news? We are called together by God and He says, “I put in you all that is in My kingdom. All the wealth. All the glory. All the majesty.”
Is there anything too difficult for the Lord? Is there a problem too big in your life? Is there a mountain too big for God to move? Is there some withholding of His hand where He can’t heal your marriage? Where He can’t heal your mind? Where He can’t rid you of that habitual pattern of sin? Where He can’t turn a despairing heart into a heart filled with joy and exhilaration and worship?
All the resources of heaven are in God’s hands and He is saying, “Oh, look! I need a firstborn son; I need a firstborn daughter! Because I want to pass on all these marvelous things to My children.”
And praise the Lord! He has passed them on to you and me! We have everything. Peter says that He has given — past tense — to us “all things that pertains to life and godliness, through the knowledge of Him who called us to His own glory and excellence” (2 Peter 1:3). Can you say amen to that?