Noajida followers inside of judaism? how can judaism accept a person who follows the God of israel?

but this person doesnt convert in a jewish, he or she considered a noajida? how can be that? are they considered like a second cl? it's strange but judaism says they are not looking for people but they are looking for people to follow the noah commands or some commands from the torah without being jewish.. I am sad that I have read some criticism from jewish people to christianity.. specially to catholicism why is that? I thought the jewish people were looking for peace?