To the church of the Thessalonians in God our Father and the Lord Jesus Christ. (2 Thessalonians 1:1)
We as a church are “in” a Father and “in” a Lord. What does that mean?
The word “Father” implies primarily care and sustaining and protection and provision and discipline. So, to be “in” the Father would mean mainly to be in the care and under the protection of God as our heavenly Father.
The other designation is Lord: We are in the Lord Jesus Christ. The word “Lord” implies primarily authority and leadership and ownership. So, to be “in” the Lord means mainly to be in the charge, under the authority, and in the possession of Jesus as our supreme Lord.
So, Paul greets the Thessalonian church in such a way as to remind them that they are a family (in the care of a Father) and that they are servants (in the charge of a Lord). These two descriptions of God as Father and Lord, and thus of the church as family and servants, correspond to two of our deepest needs.
Every single one of us has a need for rescue and help, on the one hand, and the need for purpose and meaning, on the other.
We need a heavenly Father to pity us and rescue us from sin and misery. We need his help every step of the way, because we are so weak and vulnerable.
We also need a heavenly Lord to guide us in life and tell us what is wise and give us a great and meaningful charge to fulfill, and reason for existence, some usefulness for the way God made us. We don’t just want to be safe in the care of a Father — as precious and needed as that is. We want a glorious cause to live for.
We want a merciful Father to be our Protector, and we want an omnipotent Lord to be our Champion and our Commander and our Leader in some great cause. So, when Paul says in verse 1, You are the church “in God the Father and the Lord Jesus Christ,” we can take rest and help from the one — God is our Father! And we can take courage and meaning from the other — Jesus is our Lord!