“And we know..”
This is a great promise for believers. But it is foolishness to those who do not believe – who see no real purpose in history and have no explanation for sudden death, sickness, or tragedy. It’s like a family secret that only the family of God can share together because intuitively, by the Spirit of God, we know that God has everything under control even when life seems out of control.
“all things work together for good”
This does not mean that everything that happens is good. However it does mean that God can take the good, the bad, and the ugly and work them together for our good and for His glory. The classic illustration goes like this:
You would never eat flour or shortening or baking soda by themselves. Each would taste very bad. But mix them all together in the right proportions under the supervision of a cook who knows what he/she is doing and you end up with yummy biscuits.
“to those who love God, to those who are called according to His purpose”
The promise is conditional. Believers understand that God’s ways are not our ways; His purposes are not our purposes. For example, His purpose for us is not to be happy but to be holy. Sometimes His purposes involve pain or persecution, or poverty. Those who love God and are called according to His purposes understand how these can be used of God to bring about His greater purpose of exalting His great Name.