In the Old Testament Jesus started to teach His people How to love one an other. Part of loving people is not holding grudges against them. Also He tried to teach them that revenge comes out of hatred not out of love. True love does not seek to harm another.
Many falsely think Love to be the New Testament teaching
But when we take a closer look at this
we can clearly see that love was a principle of God all along. God wants all His people in all ages to love others and to love Him.
The Jewish people as a whole rejected the loving of others and as a result rejected their Savior.