Religion Study - Abraham is the first biblical

Religion Study

Both of these questions should be answered on the basis of the biblical text as far as we have read so far.  I ask that you not do research.  But do not make things up.  Make sure you can prove anything you say with a biblical text, the more specific the better.  

Please make you answers brief:  1-2 sentences for no. 1, and a few for no. 2.

 1.  Abraham is the first biblical figure to believe (or, trust) in God (Gen 15:6).  The question is why.

In this regard, you may be misled by a comment in your HarperCollins Bible – that the description “means that he trusts God and his promise … It is … faith that takes God’s word as sufficient.”  Abraham’s response to God in v. 8, however, suggests the opposite. 

2.  In Gen 17, God makes a covenant with Abraham.  It is the second covenant in P and it is also commemorated by a “sign”:  circumcision.  Why is circumcision an appropriate sign of this covenant?