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 And the servantsof the master of the house came and said to him, ‘Master, did you not sow good seed in your field? How then does it have weeds?’