Song 5:2

2 I was asleep, but my heart was awake. It is the voice of my beloved who knocks: Open to me, my sister, my love, my dove, my undefiled; For my head is filled with dew, My hair with the dampness of the night. 

my beloved who knocks – we understand this from Rev 3:20, “behold I stand at the door and knock,” and Rev 3:8, “See I have set before you an open door . . . for you have kept My Word.” The True Church must keep Christ’s commandments, “if anyone loves Me, he will keep My word, and We will meet him and make our home with him,” (John 14:23). This provides the reason for the “disappearance” of Christ from the Great City, described in verses 6 and 7.