This used to be answered by the story of the Presbyterian and Methodist ministers who agreed to exchange pulpits the next Sunday. They met half way, and the Presbyterian said "Brother, remember you are predestined to preach in my church this morning." The Methodist turned his horse around and rode back to his own congregation! But that is an inadequate explanation.
The words PREDESTINED, GOOD, and CALLED need to be taken together. In Paul's writings predestination is not fatalism. Muslims say "Insha' Allah" which could suggest that we have no part in the outcome of what happens. Nor is Christian predestination a matter of details. We are not told what tie to wear, or whether it would be better to serve steak or lamb. It is our character that is "predestined to be conformed to the image of his Son."
That does not mean being cloned to be identical. Rather we should picture what Jesus would be and do in our situation. What if he were born with the genes we received from our parents as either male or female ? What if he had been raised with the language and social upbringing we received in our first seven years? What if, instead of working as a village carpenter, he had our training and profession?
That might enable us to see what our good will be. "All things work together for good to those who love God" (Romans 8:28). Our good is to be perfected in our own way for the perfect love of heaven. He taught us to go the extra mile, turn the other cheek, love enemies, bless people, and have a special love for our Christian family. But there are many different ways of expressing that. My wife Mollie has a wonderful prayer ministry, she uses her musical gifts, and is given to hospitality and deep friendships. I hope my love is expressed through studying the Bible and teaching in church congregations and through my web site and responses on the Internet.
The third word refers to our calling, which includes our freedom to respond or go some other way. The human story begins with the Son of God coming to invite Adam and Eve to go out for an evening walk (Genesis 3:8). They were not predestined to hide in the trees of the garden. Whether we live in a city apartment, a country mansion, a refugee camp, or a hospital bed, we can go along with Jesus the Son of God, or we can back off from our destiny.
But when we respond to his call we are immediately justified (the Greek word means "put right"). Not only are we forgiven, but we are going to be glorified each in our own way. In a garden the roses, tulips, daffodils, and lily of the valley are predestined for their own glory. The difference is that we have a freedom to refuse the sunlight, rain, and nutrients. But if we welcome God's calling to our good we are predestined to our perfection.