How could Jacob wrestle with God if no one can see God and live? Is this a contradiction? Or am I missing something. It seems strange to think one can "wrestle" with God.

Genesis 32:30 (NIV):


  30 So Jacob called the place Peniel, saying, “It is because I saw God face to face, and yet my life was spared.”


Exodus 33:18-20 (NIV):


  18 Then Moses said, “Now show me your glory.”
  19 And the LORD said, “I will cause all my goodness to pass in front of you, and I will proclaim my name, the LORD, in your presence. I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion. 20 But,” he said, “you cannot see my face, for no one may see me and live.”
So first off, this story of Jacob "struggling with God" (in Hebrew Isra - el) is one that has puzzled people for years.  There is little agreement amongst scholars about what this means.  Some interpret this is a vision, others as a theophany, and still others suggest that it was simply a metaphor for the striving and struggling that Jacob had been doing all along.

Beyond that, however, the exact question is, 'Why didn't Jacob die after seeing the face of God (the Pen - el)?'  After all, as you pointed out, when Moses asked to see God's face 430 years later, he was told that if he did, he would die.

Two theories:


God was disguised

What is different, however, is that Moses wanted to see God's full Shekinah Glory. He wanted the unmediated experience of seeing God in his fullness.

In contrast, here God is clearly not revealed in his full glory.  Remember that when the three visitors came to see Abraham, they were disguised. When the angel came to visit Samson's father, he was disguised.  When there was the fourth in the furnace, shining brightly as a 'son of God,' he too could have been considered to be disguised.

For a trickster who had disguised himself once to fool his own father, Jacob would have understood a disguise.  There's nothing supernatural here in being able to realize that someone is way more than he looks like on the surface.
It was a miracle.

Jacob himself is shocked that he saw God and lived. He was in fact, left crippled by the experience, it was that powerful.  Remember, he was blessed, though its hard to understand how being crippled is a "blessing," unless if compared to the certainty of death for seeing God face to face.  That his life was preserved and he still got to be with God in the same way Adam once talked to him is an amazing gift.