Related: For better understanding between Jews and Christians, some reading material
I think there is an important distinction to be made between the Jesus(es) that Christians believe in and the real historical Jesus.
The sources available to us are highly questionable in terms of veracity. The "gospels" were written by people who never met Jesus, and in most cases, people who never met people who met him. No eyewitness accounts exist, and it is almost certain that none were made.
The sources which do exist have been heavily redacted and revised by later scribes, largely in the interest of combating heresies (see Dr. Bart D. Ehrman's The Orthodox Corruption of Scripture).
The only aspects of the story of Jesus' life which almost all credible scholars agree are authentic are:
He was born in Nazareth.
He was an itinerant preacher.
He was baptized by John the Baptist.
He told his followers to eat bread and drink wine in memory of him.
He was crucified by the Romans as a public nuisance.
The Jesus Seminar found that the only sayings of Jesus almost certain to be authentic are:
The sayings the Fellows voted as most likely to be authentic were:
Other cheek (Q) Matt 5:39, Luke 6:29a
"But I tell you, do not resist an evil person. If anyone slaps you on the right cheek, turn to them the other cheek also."
Coat & shirt (Q) Matt 5:40, Luke 6:29b
"And if anyone wants to sue you and take your shirt, hand over your coat as well."
Congratulations, poor! (Q, Thomas) Luke 6:20, Thomas 54
"Looking at his disciples, he said: "Blessed are you who are poor, for yours is the kingdom of God."
Second mile (Q) Matt 5:41
"If anyone forces you to go a mile, go the second mile with him also"
Love of enemies (Q) Luke 6:27b, Matt 5:44b, Luke 6:32, 35a
"But I tell you, love your enemies and pray for those who persecute you,"
Leaven (Q, Thomas) Luke 13:20-21, Matt 13:33, Thom 96:1-2
He spoke another parable to them, "The kingdom of heaven is like leaven, which a woman took and hid in three pecks of flour until it was all leavened."
Emperor & God (Thomas, Mark) Thom 100:2b, Mark 12:17b, Luke 20:25b, Matt 22:21c
"20And He said to them, "Whose likeness and inscription is this?" 21They said to Him, "Caesar's." Then He said to them, "Then render to Caesar the things that are Caesar's; and to God the things that are God's." 22And hearing this, they were amazed, and leaving Him, they went away."
Give to beggars (Q) Matt 5:42a, Luke 6:30a
"Give to him who asks of you, and do not turn away from him who wants to borrow from you."
The Samaritan (L) Luke 10:30-35
"30In reply Jesus said: “A man was going down from Jerusalem to Jericho, when he was attacked by robbers. They stripped him of his clothes, beat him and went away, leaving him half dead. 31A priest happened to be going down the same road, and when he saw the man, he passed by on the other side. 32So too, a Levite, when he came to the place and saw him, passed by on the other side. 33But a Samaritan, as he traveled, came where the man was; and when he saw him, he took pity on him. 34He went to him and bandaged his wounds, pouring on oil and wine. Then he put the man on his own donkey, brought him to an inn and took care of him. 35The next day he took out two denariie and gave them to the innkeeper. ‘Look after him,’ he said, ‘and when I return, I will reimburse you for any extra expense you may have.’"
Congratulations, hungry! (Q, Thomas) Luke 6:21a, Matt 5:6, Thom 69:2
"Blessed are those who hunger and thirst for righteousness, for they shall be satisfied. "
Jesus Seminar Fellows also came to consensus on the following:
Jesus of Nazareth did not refer to himself as the Messiah, nor did he claim to be a divine being who descended to earth from heaven in order to die as a sacrifice for the sins of the world. These are claims that some people in the early church made about Jesus, not claims he made about himself.
At the heart of Jesus’ teaching and actions was a vision of a life under the reign of God (or, in the empire of God) in which God’s generosity and goodness is regarded as the model and measure of human life; everyone is accepted as a child of God and thus liberated both from the ethnocentric confines of traditional Judaism and from the secularizing servitude and meagerness of their lives under the rule of the empire of Rome.
The Jesus Seminar is rather controversial among scholars, and I think they got a lot of things wrong, but the quotes above reflect the consensus view of the academic community for the most part, although many scholars think that Jesus may have thought of himself as the messiah; in the absence of more reliable information, however, we can't say this with any certainty. It is entirely possible that Jesus never claimed to be anything but a man who was committed to strict adherence to Jewish law and scriptures.
It is widely believed that the passages from the Christian scriptures in which Jesus rejects the Halacha are later inventions by scribes who held anti-Semitic views, not accurate representations of his actual beliefs and instructions.
Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to uphold them. 18For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished. 19Therefore anyone who sets aside one of the least of these commands and teaches others accordingly will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven.
- Matthew 5
This passage is likely to reflect Jesus' own views. The laws of Moses and the teachings of the prophets are inviolable and eternal, and no one can enter the kingdom of God without reference to these requirements.
We can't say with certainty that Jesus' message was consistent with Jewish laws, but it seems very likely that this is indeed the case.
One of the most highly regarded scholars in this field summed up the majority position on the subject of the dissimilarity between the historical Jesus and the Christian Jesus as follows:
In the simplest terms, Christianity is a religion rooted in a belief in the death of Jesus for sin and his resurrection from the dead. This, however, does not appear to have been the religion that Jesus preached to the Jews of Galilee and Judea. To use a formulation that scholars have tossed about for years, Christianity is not so much the religion of Jesus (the religion that he himself proclaimed) as the religion about Jesus (the religion that is based on his death and resurrection).
- The New Testament: A Historical Introduction to the Early Christian Writings, Dr. Bart D. Ehrman
The gap between what Jesus believed and what his followers believe about him is almost certainly enormous.
Although I'm not an expert in the subject, I think it is possible and acceptable to hold positive or neutral views of the historical Jesus while rejecting the Christian Jesus, who is probably nothing like the real man. Someone who is better qualified to answer questions about Jewish law may be able to determine whether the passages quoted above are consistent with Jewish laws.