He cannot tolerate sin. He is eternally repulsed by the unholy sinfulness of His own creation. Why God deemed it suitable for all to be this way is not given for man to comprehend. It cannot be done. Though we cannot comprehend why God has so ordained things in this manner, we can be assured that the revelation of His Word, as stated in the Bible, says that He has.
Man knows but little.
Nevertheless, God, and only God, has solved the enigma He Himself has disclosed. God has sent His only Son, Jesus Christ, to live a perfect sinless life, to qualify as a perfect sacrifice, to obtain a perfect redemption so that God reconciles Himself to man. This great exchange of Jesus Christ doing for sinners what God demands of sinners is called the Substitutionary Atonement. The Gospel is the Good News that the righteousness of God has now been revealed. It is a righteousness of God that satisfies His own righteousness in order to receive sinners into His presence.