Just as the disciples on the road to Emmaus recognized Jesus in the breaking of the bread, so we, through the working of the Holy Spirit, recognize our Lord in the Word and Sacraments.
Now, in the New Testament, the number for the Church remains twelve as Jesus calls twelve Apostles to be trained by Him to carry out the ministry following His ascension.
In the Old Testament all the world is narrowed down to the people of Israel, which is eventually narrowed down to One—Jesus! Jesus is Israel reduced to one in order that all the world might be saved through Him.