The death of his wife forces Macbeth to contemplate mortality and the fragile nature of life. He realises that their evil deeds, founded in his ambition, have destroyed her. His life has lost its purpose without his 'dearest partner of greatness' and yet he has no time to mourn her passing.
Macbeth has lost everything but his life and that is shortly forthcoming. Truly, Macbeth is overwhelmed with guilt at his wife's death. After all, he did kill King Duncan and made Lady Macbeth his accomplice. No doubt, Macbeth feels overwhelmed with a sense of guilt. He did initiate the whole idea of killing King Duncan.
Regret and guilt as he feels that he has lead her to doing what she did. Distraught because he keeps wanting to blame himself for his bad actions. Choosing the immoral way than the moral way.
Macbeth's reaction to the news that his wife is dead is sadness mixed with regret. He says, "She should have died hereafter; / There would have been a time for such a word." He means that he wishes she would have died when he had the time to properly mourn her. He goes on then to bemoan the current state of his life; how everything has gone badly and life has lost its meaning. He has become a man driven by his own ambition run amuck as though he were in a car he started but now the gas pedal is stuck fully to the floor and he can't stop it. The only course of action he can take now is to try to preserve his own life because that is all he has left. And that, he observes, is pretty much meaningless.