Consider, for Paul that justification is the present faith-anticipation of the eschatological verdict. Sanctification is the Spirit-life of the future come into the present. Salvation itself is a matter of being united with Christ in his death and resurrection, which is the first fruits of the final resurrection of the people of God. The presence of the Spirit in the Church marks it out as an eschatological community. And the Mosaic Law, though it was a good thing, is now obsolete because it was intended for an age that has now ended with the coming of the Christ and the Spirit. More could be said, but you get the picture.
But why is Paul’s theology so pervasively eschatological? I am persuaded that it is because of his all-consuming focus on Christ. The first coming of Christ was an eschatological event which inaugurated the eschatological kingdom of God. His death on the cross is the decisive end of the old age; his resurrection the decisive beginning of the new. As already observed, his resurrection is also the initial phase of the general resurrection, his new life the beginning of the new creation that will find its ultimate consummation upon his return. Let’s not forget that Paul’s eschatology is not fully realized; to suggest as much would be a grave misunderstanding of his thought. But Paul did believe himself to be living at the end of the old age and the beginning of the new. And the crucial difference was the presence of the Messiah, Jesus Christ the Lord. And because of that, for Paul, eschatology is everything.