What, now, was the main purpose of it? What had the Apostle in his mind when he sat down to write? To answer that, we must go back a little way.
A great subject of apostolic preaching at Thessalonica had been the Second Advent. So characteristic was it of the gospel message, that Christian converts from heathenism are defined as those who have turned to God from idols, to serve the living and true God, and to wait for His Son from heaven. This waiting, or expectation, was the characteristically Christian attitude; the Christian's hope was hidden in heaven, and he could not but look up and long for its appearing. But this attitude became strained, under various influences. The Apostle's teaching was pressed, as if he had said, not only that the day of the Lord was coming, but that it was actually here. Men, affecting to speak through the Spirit, patronised such fanaticism. We see from chap. ii. 2 that pretended words of Paul were put in circulation; and what was more deliberately wicked, a forged epistle was produced, in which his authority was claimed for this transformation of his doctrine. Weak-minded people were carried off their feet, and bad-hearted people feigned an exaltation they did not feel; and both together brought discredit on the church, and injured their own souls, by neglecting the commonest duties. Not only decorum and reputation were lost, but character itself was endangered. This was the situation to which Paul addressed himself.
We do not need to be fastidious in dealing with the Apostle's teaching on the Second Advent; our Saviour tells us that of the day and the hour no man knows, nor angel; nay, not even the Son, but the Father only. Certainly St. Paul did not know; and almost as certainly, in the ardour of his hope, he anticipated the end sooner than it was actually to arrive. He spoke of himself as one who might naturally enough expect to see the Lord come again; and it was only as experience brought him new light that in his later years he began to speak of a desire to depart, and to be with Christ. Not to die, had been his earlier hope, but to have the mortal being swallowed up of life; and it was this earlier hope he had communicated to the Thessalonians. They also hoped not to die; as the sky grew darker over them with affliction and persecution, their heated imaginations saw the glory of Christ ready to break through for their final deliverance. The present Epistle puts this hope, if one may say so, to a certain remove. It does not fix the date of the Advent; it does not tell us when the day of the Lord shall come; but it tells us plainly that it is not here yet, and that it will not be here till certain things have first happened. What these things are is by no means obvious; but this is not the place to discuss the question. All we have to notice is this: that with a view to counteracting the excitement at Thessalonica, which was producing bad consequences, St. Paul points out that the Second Advent is the term of a moral process, and that the world must run through a spiritual development of a particular kind before Christ can come again. The first Advent was in the fulness of the times; so will the second be; and though he might not be able to interpret all the signs, or tell when the great day would dawn, he could say to the Thessalonians, "The end is not yet."
This, I say, is the great lesson of the Epistle, the main thing which the Apostle has to communicate to the Thessalonians. But it is preceded by what may be called, in a loose sense, a consolatory paragraph, and it is followed up by exhortations, the same in purport as those of the First Epistle, but more peremptory and emphatic. The true preparedness for the Lord's Second Coming is to be sought, he assures them, not in this irrational exaltation, which is morally empty and worthless, but in diligent, humble, faithful performance of duty; in love, faith, and patience.