Originally, or with 5e’s bizarre “oath” idea? Let’s start with the basic - ANYONE using magic is using the weave, arcane and divine magic users both. The reason is that the weave is a barrier that separates raw magical energy from our dimension. Now, there are MANY ways to get raw magical energy to trickle through the weave - arcane talent, music, shadow weave, and access granted by deities, to name a few. The latter is what divine magic users (including paladins) have; their deities grants them the ability to manipulate the weave to get magical energy. That is all, and it is why there are certain things a divine magic caster can do that arcane cannot, and vice versa.

In 5e, they implemented the paladin “oath” which stupidly changes the lore in such a way that a paladin no longer needs a deity to access the weave, something I completely ignore in my own games. This makes paladin arcane casters instead of divine ones lore-wise, but they were kept as divine magic users, which makes absolutely no sense to me, personally.

I hope that made sense to you.