And that ye study to be quiet dealt with the problem of mental agitation or excitement. This excitement was due perhaps to the new salvation experience and hopes which had gripped their minds. No doubt, the teaching concerning the return of Christ had much to do with their agitation as well. The apostle was not cautioning them concerning the joyful and excited attitude of being a Christian. Instead he was dealing with a fanatical frame of mind that caused them to be meddlesome and idle.
Study literally means to be ambitious for, to strive eagerly to bring something to pass.
The idea seems to be seek earnestly to be quiet. To be quiet basically means to be at rest and was used of silence after speech, rest after labor, peace after war, etc. Here it is used to urge the living of a calm restful life. The present tense of study and to be quiet stresses that they must constantly strive to lead such a life. Instead of allowing them to succumb to fanatical excitement, Paul recalled them to restfulness of mind and a balanced outlook upon life.