The Lord is a GOOD Master

Adonai means Lord or Master. It was the word used when addressing an authority (like the king) or even the master of a slave or servant. Masters were not always benevolent in ancient times (even Jesus mentioned this in Matthew 20: 25) and so it's significant that the Old Testament believers tell us Adonai is good. 

Psalm 86: 5 - Adonai tov salach - the Lord is good and forgiving.

The belief in a good Lord, a kind Master, is proclaimed several times in the psalms, but more often using Yahweh Tov than Adonai Tov:

Psalm 145: 9 - The Lord is good to all.

Psalm 34: 8 - Taste and see that the Lord is good.

Lamentations 3: 25 - The Lord is good to those who seek Him.

So, in recognising Adonai as our Sovereign Lord, we don't need to fear that He will be unkind or cruel. The Bible clearly attests that He is a Good Master to serve. When Jesus prayed, "Not my will but yours be done," He was accepting God's sovereignty in His life. But He didn't call Him Adonai at that point; He called Him Father. (Luke 22: 42)