Do the weeds remaining among the wheat mean that we cannot distinguish between true and false Christians?
No, we definitely can distinguish between true and false Christians, and we must carry out church discipline, because the church and the kingdom of heaven are not the same, for Matthew himself does not equate them (see Matthew 16:18-19); as well, Christ himself gave explicit commands regarding the exercise of discipline.
No. Matthew 13:29 does not mean that we cannot distinguish between true and false Christians, nor does it imply that church discipline should be abandoned. For apart from the fact that the church and the kingdom of heaven ought not to be regarded as synonymous—for the evangelist Matthew himself does not equate them (see Matthew 16:18–19)—it must be noted that Christ himself has given explicit commands regarding the exercise of discipline.1
27 Les serviteurs du maître de la maison vinrent lui dire: Seigneur, n'as-tu pas semé une bonne semence dans ton champ? D'où vient donc qu'il y a de l'ivraie?