Multiclassing opens up almost infinite build possibilities in Dungeons & Dragons Fifth Edition, including combinations that may seem unlikely at first. A D&D paladin's devout, oath-sworn nature can conflict with the mental image of a barbarian drenched in blood. Nonetheless, there's plenty of reason to multiclass the two.
Source:https://www.cbr.com/dnd-5e-barbarian-paladin-multiclass-guide/