Angels learn about grace through watching the church because grace is not a facet of God that angels can experience, therefore comprehend.
that through the church the manifold wisdom of God might now be made known to the principalities and powers in the heavenly places.
St. Thomas Aquinas speculates as to the truth behind this text in his commentary on Ephesians:
The means through which the manifold wisdom of God is made known to [the angels] is designated by his saying through the church. We bring nothing to the table.............
I read that verse and think that the angels are watching what God is doing, not what the church is doing.
Amen, mm. This is the point of Eph. 3:10. That we, who know the grace of God are studied by angels. They are indeed learning through us, the Church the Body of Christ. :)