"Love begets love" is an idiom/proverb in the English language that follows the principle of treating others as one would like to be treated. More plainly, it means: "If you behave lovingly to other people, they will behave lovingly to you," according to The Free Dictionary.
The dictionary definition of "beget" is "give rise to; bring about." Through loving others, the person is bringing about love and kindness in others. Though one person cannot force another to literally love him, "love begets love" is an idiom that follows the moral principle that one person should treat others as he would like to be treated. If a person is willing to love others and acts kindly towards them, then he is more likely to be loved and treated well by others.