Lady Macduff has just been informed by Ross that her husband has fled Scotland. But Ross won't divulge to her Macduff's suspicions about Macbeth and the reasons he has fled, so she assumes that her husband is behaving in a cowardly way to flee and leave his wife and children.
When Ross leaves, she tells her son that his father is dead, and yet, when the murderers barge in a few lines later, she staunchly defends her husband:
Where is your husband?
I hope, in no place so unsanctified
Where such as thou mayst find him.
And when the Murderer calls Macduff a traitor, his son defends his father -- "Thou liest, thou shag-hair'd villain!"
So, this quote you have referenced is meant to show that even though she has no idea where Macduff has gone or what the reasons for his fleeing are, she is still willing to defend him, telling the Murderer that she certainly hopes her husband would never be any place so unholy ("unsanctified") as any place that the Murderer might be able to find him, implying that her husband is too good and honorable for that.
These are the last lines of Lady Macduff in Act 4 Scene 2 of Macbeth. At the beginning of the scene, Rosse has called on Lady Macduff to tell her that Macduff has gone away. Lady Macduff is angry that her husband has left without warning and that he has not seen that the family should be protected in his absence. After Rosse leaves, the murderers enter the castle, and one of them confronts Lady Macduff. She is quite cynical at this point and tells the murderers that she will not beg for her life because harm often comes to those who have done only good. The murderer asks where Macduff has gone, and Lady Macduff tells them that she hopes that Macduff has gone to a place where he will be safe from murder.