Hebrews 1:7

And on the other hand to the angels he says, "He makes his angels winds, his servants flames of fire."

This quote is taken from Psalm 104:4

Paul here contrasts who the Son is (as presented by the OT) and who the angels are (their characteristics also presented in the OT).

In Psalm 104, God is presented as the awesome Creator, but also the Creator who is still very much active in the creation. He is seen as the one who causes rivers to flow and rains to fall. Animals are refreshed by his work. The animals of the earth are fed by the grass that he causes to grow. God is viewed not only as the Creator of life, but also Life itself. "When you give it to them, they gather it up; when you open your hand, they are satisfied with good things. When you hide your face,they are terrified;when you take away their breath, they die and return to the dust. (verses 28-29).

But in verse 4, (referred to in Hebrews 1:7) God is seen as the one who is over the angels, who he commands the wind and the flames of fire (lightening). They are his servants working and sustaining creation. They have a great place in this earth. However, the angels are still servants. In a household, no matter how important the servants are, they are not higher than the Son. Paul here shows the place of angels (a high one indeed), but contrasts that with the greater place and importance of the Son.

See how this develops in the following verses...