The Christian Gospel not only took the known world by storm, but from the perspective of social values, turned much of it upside down.
Paul, in his continuing effort to shape Corinthian Christians in accordance with their common vocation, reminds them that the call of Christ offered to all of the baptized is a call to follow him and to become signs and witnesses of the reign of God.
Now in terms of the social norms of Paulís day this would lead the majority of Christian converts to see themselves as having been selected because of their superior attributes.
Paul pulled their pedestals out from under them by suggesting that they take a good and honest look at themselves.
As a group they were less than wise, less than powerful, less than noble.
In short he says, "Most of you have nothing to boast about and that is precisely why you received you Christian vocation... a vocation that carries with it the potential for you to become TRULY wise, TRULY strong and TRULY noble."
But for this potential to be actualized you must humbly accept that the source is not your sterling qualities but rather your life in Jesus Christ.
And so Paul says to them, as well as to us, "If, from time to time, you feel that you need to boast, make sure that you boast in the Lord."
Anything else would be to revert to pagan norms and values.