# have come out of the great tribulation

"have survived the great tribulation" or "have lived through the great tribulation"

# the great tribulation

"the time of terrible suffering"

# They have washed their robes and made them white in the blood of the Lamb

"They have been made righteous by washing their robes white in his blood" 

# the blood of the Lamb

The word "blood" is used to refer to the death of Lamb.