Secular humanism and Christianity differ in their approach to ethics. Humanists believe that human beings are capable of being ethical and moral without religion or God. The humanist approach is to do the right thing because that is the right thing to do, which some theologians criticise because it requires an interpretation of what is right. The Christian approach is to do the right thing because the Bible or the Church tells Christians what to do, an approach which is criticised because the Bible's story is interpreted for Christians by the clergy.
Secular humanism also emphasises fulfilment in this life, whereas Christians believe in a life to come and believe that fulfilment must wait for the next life.