One God in Trinity

I came across some clarifying content in a book I was reading titled "The Doctrine of God". Some pretty heady stuff, but the particular info that helped me in one chapter was the background on Judaism or the Jewish religion. This was of particular interest as a new friend of mine is married to person that grew up in a Jewish home and claims to be a practicing Jew. As I grow in my relationship with Christ and process life in that lens, there has been a growing desire for me to understand the 'religious movements' in the world. So the following has helped me shape those thoughts!

"In Judaism God is one and personal, but although these characteristics are fundamental to his being, they are not the most important element in Jewish worship of him. Jews tend to be preoccupied with the holiness of God, and especially of the divine name, an attitude which is inculcated by the covenant law of Israel. The main purpose of this law is to keep Jews clean, pure and undefiled, so as to make them worthy of their calling as God's chosen people. But the restrictive legalism which this has entailed is not regarded by those who uphold it as a fetter on their spiritual liberty. On the contrary, it appears to them to be the main basis of their spiritual assurance and freedom, since only within the narrow confines of the law can Jews be assured that they are living according to God's will. The law, supplemented by the interpretations of later generations, is revered as the voice of God, through which the nation enters into a living experience of its covenant relationship with him."

"In principle, Christianity subscribes to the Jewish covenant, and the belief in a holy God which that entails. It accepts the law of Moses as a revelation of God's holiness, but argues that it cannot be used as a means of salvation. In Christian eyes, nobody can keep the law in every respect, because at the bottom the problem of human sin is that of a broken relationship with God. Only when that is put right can the spiritual character of the law begin to make sense, and become applicable to us. In putting that broken relationship right, Christians agree with traditional Jews that the atoning sacrifice provided for in the law is fundamental, but they insist that this sacrifice was made once for all by Jesus Christ."

"Jews may recognize God's existence and know his law, but without Christ, they cannot penetrate the mystery of that divine fellowship which Christians call the Holy Trinity."