Deut 23:3

23:3 Ammonite or Moabite . . . the tenth generation. As the word “forever” in this verse indicates, “tenth generation” is probably an idiom denoting permanent exclusion from the worshiping community of Israel (cf. Neh. 13:1). This special exclusion of Ammonites and Moabites was due, not to their incestuous origin (Gen. 19:30–38), but to their stubborn opposition to Israel (v. 4; Neh. 13:2). The Old Testament also looks forward to a new covenant in which the exclusions of this passage are transcended (Is. 56:3–8), an event prefigured by Ruth, the Moabite who became the ancestor of David and of the Messiah (Ruth 1:4; 4:17; Matt. 1:5).