Charles Ellicott Commentary Ruth 4:6

"And the near kinsman said, I cannot redeem it for myself, lest I mar mine own inheritance: take thou my right of redemption on thee; for I cannot redeem it." — Ruth 4:6 (ASV)

Lest I mar ... —The redemption of the land would involve the spending of money, drawn away from the Goel’s own estate; but the land thus acquired would not belong to the Goel himself, but to the son he should have by Ruth, who would still be, in the eyes of the law, the son of Mahlon. It would, therefore, be like mortgaging one’s own estate, and that for the benefit of another. Josephus and the Targum explain it by saying that he already had a wife, and feared the discord that might arise.