Granny's objective for Janie's marriage is one of safety and security. The fact that Logan Killicks owns his own property and can provide for Janie is her only concern. When Janie questions this thinking and argues for her own objective in marriage--love--her grandmother's response is clear: "It ain't love ah wants you to have Janie, it's protection."
As a former slave, Janie's grandmother's perspective on life and the world around her is much, much different than Janie's, who "wants things to be sweet with [her] marriage, like a bee to a blossom." Janie and her grandmother come from entirely different ends of the spectrum in regards to their perspective on marriage.