In light of recent (non-)events I thought I would post something on what Hebrews says about the παρουσία or second coming of Jesus. The clearest reference to the second coming is found in 9:28:
"so Christ also, having been offered once to bear the sins of many, will appear a second time for salvation without reference to sin, to those who eagerly await Him." (NASB)
Since Christ appeared (πεφανέρωται; 9:26) once to take care of sin in his sacrificial death, he will appear (ὀφθήσεται) a second time without the need to deal with the sin problem. Many scholars see here an oblique parallel to the high priest who reemerges from the holy of holies after he had made atonement on the Day of Atonement. The high priest's reemergence means that the sacrifice had been accepted.
The second more oblique reference is found in the quotation of Habakkuk 2:3 LXX in 10:37:
"For yet 'in a very little while, the one who is coming will come and will not delay.'" (NRSV)
In the original context the passage is part of God's second reply to Habakkuk's questioning. It refers to a vision that the prophet must write down since its fulfillment will not happen immediately but according to its appointed time, which will be coming soon. The author of Hebrews appears to add an article before the LXX translation ἐρχόμενος, "coming," thus making it a substantive that has messianic overtones. The author interprets the passage as a reference to Jesus' imminent return.
The third passage, found in 1:6, is even more oblique and highly disputed. The introduction to the quotation reads:
ὅταν δὲ πάλιν εἰσαγάγῃ τὸν πρωτότοκον εἰς τὴν οἰκουμένην
One interpretive crux in the passage is the placement of πάλιν. It may merely introduce another quotation, as is the author's practice elsewhere (1:5; 2:13; 4:5; 10:30). The NRSV reflects this option:
"And again, when he brings the firstborn into the world."
Or πάλιν may modify the verb εἰσαγάγῃ. The NASB reflects this option:
"And when He again brings the firstborn into the world."
If the first option is adopted, then it may refer to Jesus' incarnation, or exaltation. If the second option is adopted, then it likely refers to the second coming of Jesus into the "inhabited world." On this reading, God commands the angels to worship Jesus upon his return.