'Mystery of God' in the Bible

"Can you fathom the mystery of God? Or can you probe the limits of the Almighty?

I, therefore, brethren, when I came unto you, came, not with excellency of discourse or wisdom, declaring unto you the mystery of God;

That their hearts might be comforted, being knit together in love, and unto all riches of the full assurance of understanding, to the acknowledgement of the mystery of God, and of the Father, and of Christ;

And without controversy great is the mystery of godliness: God was manifest in the flesh, justified in the Spirit, seen of angels, preached unto the Gentiles, believed on in the world, received up into glory.

But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished, as he hath declared to his servants the prophets.