Acts 15: what is necessary to be saved?

After many gentiles have believed in Jesus, Christian-Jews were saying that they should be circumcised in order to be saved. If I were living at that moment, I think that  would want to be circumcised due to the way I treat my health. When I don´t know exactly what to do in order to get something, I am careful -  so in order to have more assurance, I would agree on being circumcised. But, according to Paul, it would be an error. This kind of thought shows lack of trust that the blood of Christ is enough for me to be ok with the Lord.
However, I suppose that things are quite more complex.
James, the brother of Jesus, said:

19-21 “So here is my decision: We’re not going to unnecessarily burden non-Jewish people who turn to the Master. We’ll write them a letter and tell them, ‘Be careful to not get involved in activities connected with idols, to guard the morality of sex and marriage, to not serve food offensive to Jewish Christians—blood, for instance.’ This is basic wisdom from Moses, preached and honored for centuries now in city after city as we have met and kept the Sabbath.”

A Christian is one who belongs to Christ, who loves the Lord and loves other human beings. In doing so, his own body belongs to the Lord and he is to be in harmony with others. James was looking to how the Lord made a covenant with all the humanity and set it to all non Jews.