Jamieson, Fausset and Brown on Ruth 2:22

22. Naomi said unto Ruth ... It is good ... that thou go out with his maidens--a prudent recommendation to Ruth to accept the generous invitation of Boaz, lest, if she were seen straying into other fields, she might not only run the risk of rude treatment, but displease him by seeming indifferent to his kind liberality. Moreover, the observant mind of the old matron had already discerned, in all Boaz' attentions to Ruth, the germs of a stronger affection, which she wished to increase.