Does Matthew 9:14–17 mean that it is a mistake to try to mix the Old Covenant law with the New Covenant gospel?

The extreme discontinuity between the law and the gospel is popular among dispensationalists, but was never a part of the teachings of Jesus. Matthew 9:14–17 simply means that it would not have been appropriate for the disciples to mourn (symbolized by fasting) while Christ was with them, for He was the central figure—the prophesied Davidic King—of all promises of hope for Israel and the world. Christ uses three parables to illustrate the inappropriateness of mourning (fasting) while He is present: 1) the bridegroom’s attendants (verse 15); 2) the new patch and the old garment (verse 16); and 3) the new wine and the old wineskin (verse 17). Christ is saying that mourning (fasting) while the Source of hope is present is as inappropriate as putting new, fermenting wine into old, hardened wineskins; or as putting a patch of unshrunk cloth on an old garment; or as the bridegroom’s attendants mourning while the bridegroom is present. John the Baptist’s purpose was to call the people to repentance, which involved mourning and fasting, in preparation for Christ’s coming. But once Christ had arrived, it was time for His followers—those who had longed for His presence—to rejoice.