1)
Why does it say "I will rejoice to benefit them"?
1.
Malbim: The Bris obligates Me to constantly benefit them. If they would sin, I would not rejoice to do so. "Sas" is openly showing Simchah.
2)
Why does it say "b'Chol Libi"?
1.
Malbim: If they would sin, My heart would not cling to them.
