How Small is the Gap between Judaism and Christianity! and how Big it is!

I spoke to a group of pro-Israeli Christian students, and someone asked me to define the difference between our religions. Superficially, there are many types of Judaism and Christianity, often overlapping; for example, there are professedly religious Jews who defy Sabbath and the Christians who observe it. Reformist Judaism follows much of the practices of Lutheran Christianity.
The issue of Jesus’ resurrection is insignificant. Suppose for a moment that Jews accepted the resurrection as historical fact. What next? How does that change our life? Shall we abandon the commandments? No. Jesus told the crowd to do as the Pharisees teach, and that included the Oral Law. Shall we follow an arbitrary apostolic set of rules? But James commanded to abstain from blood; he told nothing about murder or stealing. Shall we assume those are not prohibited in Christianity? Shall the rule of positive reciprocity direct us? But how? Good Christians killed good Jews out of love for the fellow Christians. Love everyone is too vague to be practiced. Israel does not live with the Basic Law only, nor does America with the Bill of Rights. People need more detailed instructions. In Judaism, those are the commandments. Small communities of early Christians might abandon the law; their members were sufficiently close to love each other. When Christianity enlarged, some commandments were arbitrarily reintroduced. Christians rejected at least one of the Ten Commandments, the Sabbath, but accepted interpretative commandments like prohibitions of homosexuality and usury.
The real difference is practicality. Judaism is practical, Christianity - idealistic. The social teaching of Judaism is based on negative reciprocity, Do not do unto your neighbor what is hateful to you. Christianity enhanced that rule just a bit, and made it impractical. Positive reciprocity, Treat your neighbor as yourself, especially when neighbor means everyone, is unworkable. We cannot feed everyone before sitting at our own meal, nor could we help all the needy before buying non-essential goods for ourselves.
Idealism sounds great, but it is not. People who cannot practice the rules abandon them. They need to rationalize the failure. The rule of positive reciprocity cannot be possibly wrong, and so they find wrong with its objects. People not loved become demonized: even good Christians who practice great rules are unable to love such people. Hatred to aliens is another side of the universal love. Christians cannot love Jews who reject their teaching; many, therefore, hate the Jews.
Christian idealism caused problems to Jews. Leftist political idealism of love and good faith settlement with the enemies might prove as bad.