Christ is talking about the Gentiles. They will not replace the Jews, but both Jew and Gentile will be brought into the new order, the New Testament church of Jesus Christ.
‘Other sheep I have, which are not of this fold.’ Now, the Greek here is ‘fold’ or ‘sheepfold’. ‘Them also I must bring, and they shall hear my voice; and there shall be one …’ – our translation says ‘fold’ at this point, but it isn’t ‘fold’ in the Greek; it is ‘flock’. This is one of these very rare slips that we find in our grand old version, and the whole sense of the verse rests on realising the difference. By our Authorised Version translating ‘fold’ in both cases it has lost the sense which is a shame, but the Greek for the second ‘fold’ is ‘flock’. There is no difference between Jew and Gentile now, and some Christians don’t understand this. They are taught quite wrongly that somehow the Jews are still everything, and one day there will be a special provision for them. ‘But no,’ says Christ. ‘Other sheep I have’ – Gentile converts. ‘They are not of this Jewish sheepfold, and I must call them too’, and then the converted Jews will come out of this fold and together with converted Gentiles will be all one flock in a new fold.