1. The God who searches is a God of love. His desire is to have a loving relationship with us.
For God so loved the world, that He gave His only begotten Son, that whoever believes in Him should not perish, but have eternal life. John 3:16
2. However, the God who searches is also a God of perfection. His absolute moral perfection is the standard upon which the relationship is based.
Therefore you are to be perfect, as your heavenly Father is perfect Matthew 5:48
Imagine you are given a glass of cold, refreshing water.
Just before you put the glass to your lips you are told that a small drop of cyanide has been added to the water. However, since it is such a small amount of cyanide, you needn't worry. What harm can such a small amount of poison do to a full glass of cool, clear water?
But you know that no matter how small the dose of poison, it contaminates the whole glass of water. In the same way, God cannot allow even a small amount of sin into heaven lest it contaminate the entire place.