Well why pick out the issue of divorce specifically? Look at Jesus's entire teaching, Christ was much more lenient than the teachers of the Law in his day. In Matthew 9 when he's with the Tax collectors and the outcast he tells them "Go and learn what it means I will have mercy and not sacrifice" and that "I have not come to call respectable people, but outcasts"(Matthew 9:12-13)

We know during Jesus's day there were two schools in Pharisaical Judaism. The House of Hillel and House of Shammai. Shammai emphasized a strict, legalistic approach to the law. Hillel emphasized a more liberal approach to the Law that focused on it's heart. Christ and his disciples and apostles were clearly influenced by the teachings of Hillel and clashed with the conservatives and legalists of their day.