The simplicity of the letters is due not to immaturity in Paul but to immaturity in the Thessalonian church.
But the glad tidings of Thessalonian faith and love swept it at once away.
Paul practiced what he preached when he urged the Thessalonian Christians to "pray without ceasing."
All this was included in the precious gospel which Paul preached, and which the Thessalonian converts received.
For what, then, were the Thessalonian disciples taught to wait?
Such, however, was the faith of the Thessalonian Church; such is the tone and spirit of the Epistle.
The decisive moment of the crisis therefore necessarily falls between the Thessalonian and Galatian Epistles.
At any rate the simplicity of the Thessalonian epistles must not be exaggerated.
Who can say that Epaminondas could have defeated the Spartans twice without his Thessalonian cavalry.
If you had asked a Thessalonian Christian what he was waiting for, what would have been his reply?