It must be remarked that the words rendered "appear" in Hebrews 9:24-28, are three different words in the Greek.
1. The past appearing (Hbr 9:26). Here the word "appear" means, for one to be seen who had been hidden, as when one comes from behind a curtain which had concealed him.
2. The present appearing (Hbr 9:24). The term here indicates appearing in an official sense. Christ now appears in the presence of God, as the Representative of His people, to plead on their behalf, and to look after their interests.
3. The future appearing (Hbr 9:28). Here it signifies to see face to face, as when Paul saw Jesus, when he was on his way to Damascus (1Cr 15:8).