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?