You're confusing Old Testament verses about Israel with New Testament verses about Christians. God never promised healing in the New Testament. God made promises to Israel that he never promised Christians. For example,

(Deuteronomy 7:13-15 NIV) He will love you and bless you and increase your numbers. He will bless the fruit of your womb, the crops of your land--your grain, new wine and oil--the calves of your herds and the lambs of your flocks in the land that he swore to your forefathers to give you. {14} You will be blessed more than any other people; none of your men or women will be childless, nor any of your livestock without young. {15} The LORD will keep you free from every disease. He will not inflict on you the horrible diseases you knew in Egypt, but he will inflict them on all who hate you.

God doesn't promise us healing. Godly people still get sick. They can still die young. My first wife and I had two stillborn children. She died from complications due to kidney disease when she was 30. I couldn't begin to tell you about all the people who prayed for her. I also couldn't begin to tell you about all her suffering in her short life. God is still good. God has purposes for everything for those that love him.

(Philippians 4:13 NIV) I can do everything through him who gives me strength.