In other words, the sinners in heaven are there because they have been cleansed and purified by the blood of Christ. It is Jesus, His blood, His sacrifice, which called the church into being. And, it is only because of Christ that the church is redeemed and can appear before the throne of God. This is true for all, for everyone in that multitude, whether they are red or yellow or black or white, they all need to be cleansed by the blood of Christ. God's angels are there.
Believers are there.
And, Jesus is also there. Heaven is where our Savior is. Where He is, there we shall also someday be. I am going there to prepare a place for you. And if I go and prepare a place for you, I will come back and take you to be with me that you also may be where I am.