THE WORD “peculiar” is found in Titus 2:14. Christians are the peculiar people of God. We use the word sometimes when we speak of something odd or strange. But that is not its use here.
The word is translated from a Greek word which is made up of two words, one which means “around, “ as a circle, and the other which means “to be. “ It can be charted by a dot within a circle. This will help us to understand the meaning of the combined word. As the circle is around the dot, so God is around each one of His saints. The circle monopolizes the dot, has the dot all to itself. So God has His own all to Himself. They are His own private unique possession. He has reserved them for Himself.
The expression in 1 Thessalonians 1:1, “The church of the Thessalonians in God, “ has in it the same idea, for the Greek case is locative of sphere. That is, it is in the sphere of God, circumscribed by God, surrounded by Him.