"Let us
The "us" is the happy couple celebrating their marriage (see previous verse). The groom always has given GLORY to Him (God, the Father - John 5:17-47). So this request is mostly likely a reminder for the BRIDE.
for the MARRIAGE of the LAMB has come and
When we become a believer in Christ, the engagement period leading up to this marriage begins. This is a spiritual marriage and has nothing to do with the physical urges that drive so many of the earthly marriages (Matthew 22:23-30-33).
Note that "the LAMB" is previously used for Jesus Christ in the Revelation (Revelation 5:6 and Revelation 14:1).
His BRIDE has made herself READY."
Who is the BRIDE? From a Revelation viewpoint, she is
As we can see, there is no distinction as to race, religious affiliation, social status, or wealth. Thus for the BRIDE to make herself READY must be something other than that. It is left to the reader to determine how the BRIDE has gotten herself ready.
An interesting aside: while the BRIDE is referred to in the feminine form here, it probably is to reinforce the concept of believer procreation. That is, it is the female side of human beings which bears the child. In the same manner, believers beget other believers when the Gospel is proclaimed with the help of the Holy Spirit (John 3:1-5-21). This partially explains why it seems more difficult for male believers to witness to others about Salvation. They aren't use to being child bearers.