The Lord of everything leads with mercy.
Why mercy comes right after lordship
Straight after naming Allah as Lord of all the worlds, the servant names His mercy again. In the same hadith of the divided prayer, Allah answers this line: My servant has glorified Me.
Think of the most powerful person you know: a manager, a landlord, a judge. Power usually makes people nervous. Here the One with all power introduces Himself by mercy, twice. That is who you are speaking to when you stand to pray.
Someone that powerful must be waiting to punish me.
The One who owns everything chose to be known first by His mercy.
Remember one mercy you received this week that you did nothing to earn. Thank Him for it.