What’s so great about being a peacemaker? Why am I blessed in being a peacemaker?

Answer: “… for they will be called sons of God.”

“Sons of God” and “Peacemakers” are synonyms. 

Peacemaking is a core value of the Kingdom of God to the extent that it is effectively our nickname. It’s comparable to how certain items are called by a certain name, regardless of the brand used – i.e. Kleenex vs. facial tissue or Uber vs. rideshare.

It’s a blessing to be a peacemaker because it’s proof for you that you are who you say you are (a son of God), and it’s a way (like mercy is a way) of seeing the Kingdom of God come to bear on this world. 

Reconciliation is Gospel-evidence. Peacemaking is evidence that who Jesus is and what He has done is real.

Paul put it this way in 2 Corinthians 5:18-19. 
18 Everything is from God, who has reconciled us to himself through Christ and has given us the ministry of reconciliation. 19 That is, in Christ, God was reconciling the world to himself, not counting their trespasses against them, and he has committed the message of reconciliation to us.

When we do the work of peacemaking, we are pointing to the greatest act of peacemaking.

Therefore, since we have been justified by faith, we have peace with God through our Lord Jesus Christ. (Romans 5:1)