And his arrogance increased as he never thought it his wildest dream that what the apparitions said to him would come true, specifically the prophecy about "no man born of woman will harm MacBeth." So when he heard about Birnam Wood approaching the castle he wasn't concerned. However, we know that pride was before his crash when he learned what that prophecy really meant for him. Even then MacBeth thought he could outwit was was already forordained for him.
At first, Macbeth feels confident that no harm can come to him unless the prophecies of the witches come true. He has no fear. He's playing the part of a despicable tyrant to everyone around him. Those who still serve him do so out of fear rather than loyalty. He's arrogant, calling his servants cowards, and he considers the opposing army to be lazy and self-indulgent. He appears to lose courage temporarily after he's told a large army is approaching, but then he dismisses the news, just as he dismisses the news of the doctor concerning his wife.
Macbeth's attitude is that of a vexed, worried man, over-confident yet anxious. Eventhough he had full faith in the Witches prophecies, he sub consciously knew that he had understood their prophecies on their face-values and that they had probably meant a LOT more than was obvious from the words that they used. This built and gave way to innate tension and worry. And like most people, he intended to cover up his worry and anxiousness by a cloak of frustration and anger. He was in a rage with his servants and soldiers. He oozes over confidence when he is told that a large army is approaching by dismissing it for unreal. He also asks the doctor to being his land to health by examining its urine and then, curing it off its sickly disease (that of war and impending doom). When the doctor tells him of his wife's health conditions which could not be cured by any kind of mdeicine, he dismisses off that news as well.