‘We have dealt very corruptly against thee, and have not kept the commandments, nor the statutes,…which thou commandedst thy Moses…If ye transgress, I will scatter you abroad among the nations.’

From the above phrases, it is obvious that the Jews were the first to break the commandments of God. As the Jews transgressed against the commandments of God, it caused God to execute His judgement against them to cause them to scatter abroad among the nations. As God was the one to execute His judgement against them, the scripture refers Him to be great and terrible. However, the problem that caused God to be terrible lied upon the sins of the Jews. If you would mention God was terrible, the Jews had to be blamed since they were the worse terrible people who had dealt very corruptly against Him.