Likewise, I say unto you, there is joy in the presence of the angels of God over one sinner that repenteth.
Note 2 at Lu 15:10: In the parable of the lost sheep, Jesus said there is joy in heaven "over one sinner that repenteth" (Lu 15:7). That could include any or all of His creation in heaven. However, in this parable He said the joy is in the "presence" of the angels. This would probably refer to the saints who have already gone on to be with the Lord as the ones who are rejoicing. While there is no reason to doubt that angelic beings rejoice at the new birth, it would certainly be understandable how someone who has experienced God's forgiveness firsthand would have even more reason to rejoice at the salvation of the lost.