Mormon returns to the theme of miracles, which will characterize true believers. These miracles will be present among true believers (and by implication in the true church), because true faith is present.
Reference: The language here echoes Mark 16:17–18:
And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues;
They shall take up serpents; and if they drink any deadly thing, it shall not hurt them: they shall lay hands on the sick, and they shall recover.
The meaning fits into Moroni’s discourse, but the language is influenced by the New Testament.