Eschatology is "doctrine of the last things." It deals with the teaching or belief, that the world-movement, religiously considered, tends towards a definite final goal, beyond which a new order of affairs will be established, frequently with the further implication, that this new order of affairs will not be subject to any further change, but will partake of the static character of the eternal.
Vos stated that the purpose of the treatise was to investigate the extent to which Paul's eschatological teaching was tied to his doctrine of the Holy Spirit. This allowed Vos both to build upon the biblical theological insights of his "Theology of Paul" and to answer the questions that he had raised in his review of Kennedy's St. Paul's Conception of the Last Things. In setting forth the grand structure of Paul's teaching, Vos asserted that Paul taught that the future world had projected itself into the present life. Vos said, "Through the appearance of the Messiah, as the great representative figure of the coming aeon, this new age has begun to enter into the actual experience of the believer. He has been translated into a state, which, while falling short of the consummated life of eternity, yet may be truly characterized as semi-eschatological."
Vos turned to Romans 1:3-4 to answer the question of how the Spirit was conferred upon Christ. He concluded that it was a history of redemption question (a contrast between the states of humiliation and exaltation) and not a question of natures (humanity and divinity). That is, the reference was not to two coexisting sides in the constitution of the Savior, but to two successive stages in his life. According to the flesh, Jesus descended from David. According to the Spirit, Jesus was declared to be the Son of God in power by his resurrection from the dead.
The Apostle Paul understood that the subsequent state, the age to come, had intruded into the present age. Paul also understood that the soteric movement that had Christ at its center occurred within this cosmical setting of the overlap of the ages. The result was a philosophy of history where eschatology no longer formed one item in the sum-total of revealed teaching. Vos's purpose in the book was to show that unfolding Paul's eschatology meant unfolding Paul's theology as a whole.