How do Banquo's thoughts and actions reveal that he is very much aware of morality and the Christian idea of good vs. evil in Macbeth?
We first see these traits in Banquo in Act I, Scene iii when he and Macbeth are first introduced to the witches. They greet Macbeth by calling him Thane of Cawdor, and then say he will be king. Macbeth and Banquo are shocked a few moments later to be told that Macbeth has received that title. Banquo's response to this news is:
[Aside to Macbeth.] That, trusted home,(130)
Might yet enkindle you unto the crown,
Besides the Thane of Cawdor. But ’tis strange;
And oftentimes, to win us to our harm,
The instruments of darkness tell us truths,
Win us with honest trifles, to betray's(135)
In deepest consequence—
Banquo warns Macbeth that the witches are evil and could be using the empty promises of power to lure Macbeth into doing things that will lead to his destruction. This, of course, foreshadows exactly what will happen, but this also shows that Banquo recognizes that within each of us resides the capacity for evil, and we must resist the temptations of evil, such as the lust for power.