Psalm 148:2 (ESV)

2 Praise him, all his angels; praise him, all his hosts!

As a further elaboration of Psalm 148:1, those dwelling in heaven are now called to praise the Lord.

These heaven-dwellers are called angels (heralds) and hosts. The first name or designation points to the serving work of the angels, the second name points to power and prowess to do battle by the angels.