Ruth 4:13 - Matthew Poole's English Annotations on the Holy Bible

Boaz took Ruth; which he might do, though she was a Moabite, because the prohibition against marrying such is to be restrained to those who continue in the heathenish estate, as is evident from the reason of it; whereas Ruth was a sincere proselyte and convert to the God and faith of Israel. He went in unto her, i.e. had conjugal converse with her. See Genesis 6:4. Conception, i.e. strength to conceive and retain seed.