Macbeth is described as brave and fearless in battle:
For brave Macbeth
—well he deserves that name—
Disdaining fortune, with his brandished steel,
Which smoked with bloody execution,
Like valor’s minion carved out his passage
Till he faced the slave (I.2.16-20)
Also as ruthlessm, since he killed his opponent without hesistation or second though:
Which ne'er shook hands, nor bade farewell to him,
Till he unseamed him from the nave to th' chops,
And fixed his head upon our battlements. (I.2.21-23)
He is described as the goddess of war's very husband:
Till that Bellona’s bridegroom, lapped in proof,
Confronted him with self-comparisons,
Point against point, rebellious arm 'gainst arm,
Curbing his lavish spirit; and to conclude,
The victory fell on us. (I.2.54-58).
He also described as the new Thane of Cawdor, though Macbeth himself doesn't know it yet:
No more that thane of Cawdor shall deceive
Our bosom interest: go pronounce his present death,
And with his former title greet Macbeth.
Alot is revealed about a character in the way others describe him. At this point in the play we have not yet encountered Macbeth, but already we know that he is highly capable in battle and respected by the very king. He is granted a title to add to his honor, since the king just found out tha the previous Cawdor had betrayed him. We expect to encounter a great man upon the introduction of Macbeth in the following scene.