God's greatest desire for us is to make us more like Jesus. It doesn't mean we won't be happy but there's always trouble in life. Sometimes it's the health of our family members. There seems to be an unusual amount of health problems in pastors' families.
You're absolutely right in that; He's molding us to be more like His son, Jesus. The devil tends to go after God's children, especially those who are doing His work. I thought of 2 passages that talk about that:
Be alert and of sober mind. Your enemy the devil prowls around like a roaring lion looking for someone to devour. Resist him, standing firm in the faith, because you know that the family of believers throughout the world is undergoing the same kind of sufferings.
--1 Peter 5: 8-9
Not only so, but we[c] also glory in our sufferings, because we know that suffering produces perseverance; perseverance, character; and character, hope. And hope does not put us to shame, because God’s love has been poured out into our hearts through the Holy Spirit, who has been given to us.
--Romans 5: 3-5