Jamieson, Fausset and Brown on 1 Timothy 5:8

8. But--reverting to 1Ti 5:4, "If any (a general proposition; therefore including in its application the widow's children or grandchildren) provide not for his own (relations in general), and especially for those of his own house (in particular), he hath (practically) denied the faith." Faith without love and its works is dead; "for the subject matter of faith is not mere opinion, but the grace and truth of God, to which he that believes gives up his spirit, as he that loves gives up his heart" [Mack]. If in any case a duty of love is plain, it is in relation to one's own relatives; to fail in so plain an obligation is a plain proof of want of love, and therefore of want of faith. "Faith does not set aside natural duties, but strengthens them" [Bengel].

worse than an infidel--because even an infidel (or unbeliever) is taught by nature to provide for his own relatives, and generally recognizes the duty; the Christian who does not so, is worse (Mt 5:46, 47). He has less excuse with his greater light than the infidel who may break the laws of nature.