When Paul begins to teach about spiritual gifts, he first seeks to make very clear the fact that no man can truly say that Jesus is Lord except by the power of the Holy Ghost.
Paul specially strongly asserts this powerful evidence of the Holy Ghost in every believer who proclaims Jesus as Lord. And yet it is something that we take for granted and pass over.
But Paul wants us to be sure to understand this: that we can only know and trust and proclaim truth about Jesus by the work of the Spirit within us.
Thus, what passes for us as something obvious to be believed, is now understood as only by the miraculous power of the Holy Ghost within us!
How sad that we get so distracted by the miraculous "sign miracles" of the Spirit that we fail to grasp the unspeakable miracle of faith and knowledge in the Lord! The whole world is filled with people who will never understand or trust in those things that we now see clearly. But we only see and know them because the Holy Ghost has wrought powerfully in us, to raise us up from the dead, to open our blind eyes, to make our stony hearts fleshy, so that we may be new creatures, able to discern, know, and believe spiritual truths that are the words of life to us!
Thus, every thing we do or that is done in us toward Christ and in love of God is a miraculous work of the Spirit in us.
The wonder is not that men will not believe, for that is the natural consequence of sin and the fall. No, the wonder is that we see and we believe and we trust and we speak wonderful truth about our Savior. That miracle is wrought by the Spirit.
As Jesus taught, this spiritual work is silent and secret, but because of it we trust in Him!