Genesis 18:9-15: God knows.

” ‘Where is your wife Sarah?’ they asked him.  ‘There, in the tent,’ he said.  10 Then one of them said, ‘I will surely return to you about this time next year, and Sarah your wife will have a son.’  Now Sarah was listening at the entrance to the tent, which was behind him. 11 Abraham and Sarah were already very old, and Sarah was past the age of childbearing. 12 So Sarah laughed to herself as she thought, ‘After I am worn out and my lord is old, will I now have this pleasure?’  13 Then the Lord said to Abraham, ‘Why did Sarah laugh and say, “Will I really have a child, now that I am old?” 14 Is anything too hard for the Lord? I will return to you at the appointed time next year, and Sarah will have a son.’  15 Sarah was afraid, so she lied and said, ‘I did not laugh.’  But he said, ‘Yes, you did laugh.’” NIV UK

God knows everything about us, but still loves us. This is not an excuse for sin, nor should it be a motivation to spiritual complacency. But it should cause us to be grateful that we are deeply loved; that we are engulfed in an unfathomable sea of mercy; that grace is all around us. Sarah’s laughter, and her lying, were known to God. This did not stop Him keeping His promise regarding Isaac. How good is our God.