A.T. Robertson Commentary 1 Corinthians 7:37

"But he that standeth stedfast in his heart, having no necessity, but hath power as touching in his own heart, to keep his own virgin [daughter], shall do well." — 1 Corinthians 7:37 (ASV)

To keep his own virgin daughter (τηρειν την εαυτου παρθενον). This means the case when the virgin daughter does not wish to marry and the father agrees with her,

he shall do well (καλως ποιησε).