There are some things Jews can believe about Jesus. We can believe that he was a Jewish man who lived during the first century CE. He was well versed in the ways of the Pharisees, who he often quotes. (Do unto others as you would have them do unto you is a paraphrase of a statement by the Pharisaic elder Hillel.) He preached a unique message of economic justice, faith, and acceptance during a time of great social upheaval in Palestine under increasingly oppressive Roman rule. He was killed by the Romans as a Jew, crucified like many other Jews of his time.
We can also believe that if Jesus were alive at the time, he would have condemned much of what has been done in his name, from the Crusades to the Inquisition to the pogroms of Eastern Europe, etc., etc.
There are other things Jews cannot believe about Jesus.
A Jew cannot believe that Jesus is the messiah, died for our sins, is part of the God head, or is the intermediary of our prayers. Period. Each of these faith statements may be essential elements of Christian faith but they are an anathema to Jewish belief. That is why the earliest Christians, who were Jews, were excised from the Jewish community. Anyone who believes these things is a Christian by faith. Anyone born Jewish who accepts these beliefs becomes a Christian and an apostate. Those who claim otherwise are either innocent victims or conscious perpetrators of deceptive marketing.
Some of my best friends are Christian ministers. (Really). We recognize what we share and share where we differ. That is different than trying to merge the differences in a way that falsifies both religions, which is what the self-named Hebrew Christians or Messianic Jews do.
We Jews allow for a great variety of beliefs. But there are some things that are outside the boundaries of what it means to be Jewish. A Jew does not need to believe in God to be a good Jew. But a Jew who believes God became a man, in the form of Jesus, is not a good Jew. For, to a Jew, God is before and beyond the world and never a physical part of it.
The followers of Jesus, particularly Paul, founded a new religion in his name. They wrote and transmitted a scripture that canonized his story and the story of his followers. They brought monotheism to many peoples around the world. According to Maimonides, this spread of monotheism through Christianity (and, he adds, Islam) was part of God’s plan to spread monotheism.
As Jews, we also believe that God is the Creator and is the God of all the peoples of the world and cares for all of them. One need not be Jewish to be a good person. According to Judaism, the righteous of all the nations go to heaven. We have the most in common with those of the Christian faith, in that we share much of the same scripture and history. Yet we have very great theological differences as well. The best interfaith dialogues are those that look not just to what we have in common, but where we differ as well.