Why is the word 'again' important in relation to Christ's sacrifice?
The word 'again' is important because it warns against repeating Christ's sacrifice. Hebrews stresses that Christ did this once, and He will not come back a second time to go to the cross. That work was accomplished at one time, and nothing can ever cross that over.
Les explains that the key word in this section is 'again.' All through Hebrews the word 'once' appears, showing that what Christ did was done once and is not repeated. Christ is not going to come back a second time to go to the cross. That was accomplished at one time, and nothing can ever cross that over. Therefore the emphasis is: beware that you do not take my Son back. The word 'again' is crucial because we are not going to repeat something that has been done once before.
So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.