God swore by his holiness

Psalm 89:30-37
The Lord make covenant with David -his line will continue forever, God swore by his holiness.
If his sons forsake the law of God and do not follow statutes of the Lord, the Lord will punish their sin with rod , their iniquity with flogging, but the Lord will not take his love from them, nor will ever betray his faithfulness.
The psalmist sings the story of God's faithful love to Israel; his covenant and promise to David of an everlasting dynasty of kings.
Why?
God is higher than everything, He created the whole world, so he swore by his holiness,
The Lord is faithfulness and full with love, he will punish his sons with rod, but the Lord will let the line of David continue forever. He will establish the kingdom of Jesus forever. The Lord will establish Israel also.
How?
Trust in Him, He is the Lord, my king forever. He never forsake me for his faithfulness.