Mr Beaver relates that Tumnus was taken north, which means to the witch. She lives in northern Narnia, and north is the "death direction" in Scripture, too (Leviticus 1:11; Jeremiah 1:14-15). She turns hearts to stone (Ezekiel 36:26).
The wise beavers know the witch is stronger than them, but that Aslan is stronger than the witch. He is the King. "It is he, not you, that will save Mr. Tumnus." "The quickest way you can help him is by going to meet Aslan."
"Did we in our own strength confide, our striving would be losing
Were not the right man on our side, the Man of God's own choosing."
They have Isaiah-like prophecies of his advent, bringing joy and chasing sorrow away. Aslan is a lion (of the tribe of Judah?), which means "'Course he isn't safe. But he's good. He's the King, I tell you."
Peter is a faithful Adam, showing us how to relate to God: he may be frightened to meet him because of who Aslan is and who Peter is, but he is longing to meet him anyway.
Even though they can do nothing without Aslan, that doesn't mean they do nothing at all. Adam's flesh and bone must sit on the throne. Beaver assumes things are coming to the end, but they aren't, just as many followers of Jesus may have thought the kingdom would be consummated by Him at His first Advent.
The witch is not human, but half giant, half Jinn. Lewis mentions Adam's first wife, Lilith. I know little about this myth, so pass over it for now with a curiousity-furrowed brow. Anyway, the witch pretends to be human, always a bad sign - Messianic imposters, false Christs.
They notice Edmund is gone, and Mr Beaver shows his wisdom further. He could tell Edmund was on her side almost by looking at him: "something about their eyes." Only Aslan can help them. Knowing the tenacity of the witch to capture them, they haven't a moment to lose before running to Him.