Torah Temimah citing Rus Rabah: One should pursue to get a Brachah from a Chacham. Rus was 40, and did not have children ¹ , and once this Tzadik prayed for her, she was Nifkad (became pregnant very shortly afterwards).

Rashi: What she did with her mother-in-law.

Malbim: She chose to marry a Yisrael (Machlon). He was young; perhaps you desired his beauty. The latter Chesed is that you want to do with the Nefesh of your husband, via Yibum. For this, you chose an old man, rather than pursuing a young man. Even a poor youth is better than an old man ¹ . You could have found a rich youth to marry you, due to your beauty, and you chose an elder in order to sustain your husband's name!