I'd also recommend the video above. Wolfmueller is great and does a fantastic job in explaining Lutheran doctrine!
I can also sum up the Lutheran position on the occupation of good angels as: They serve and worship God, executing His will and acts as messengers; they minister to the Church for the protection and guidance of her members. They watch over us, but we do not invoke or call upon them, but always upon the name of Jesus, who, in His good pleasure, sometimes acts through His angels. In Scriptures, we find that God is called YHWH Sabaoth - LORD of Hosts (or LORD of Angel Armies).
Better yet, the Lutheran position can simply be summed up in the words of Hebrews 1:14: "Are not all angels ministering spirits sent out to serve for the benefit of those who are going to inherit salvation?"