When copying from 𝓞 into 𝓟, Oliver Cowdery initially omitted a whole clause in this verse. His eye must have skipped down from the first Holy Ghost to the second one. He seems to have caught his error almost immediately; the long supralinear insertion was written without any change in the level of ink flow.
Summary: Maintain in 2 Nephi 31:13 the longer, corrected reading in 𝓟.