The doctrine of the holy angels must be drawn not from reason, according to which their existence is at best only probable, but alone from Scripture, which from Genesis to Revelation teaches their existence, Gen. 3, 24; 32, 1. 2; Ps. 104, 4; Rev. 12, 7. In other words, also of this doctrine Scripture is the only principium cognoscendi. Modern rationalistic theology rejects the doctrine of the angels ("There is no personal devil. Even the existence of good angels cannot be proved"), just because it has discarded Scripture as the only source of faith.
However, while Holy Scripture clearly teaches the existence of angels, it does not state definitely the time of their creation, though this was within the hexaemeron. Certainly the angels were not created before the world, since prior to the creation no creature existed, John 1, 1-3; Col. 1, 16. Nor were they created after the sixth day of creation, since God on that day ceased to create, Gen. 2, 2. 3. Scripture informs us definitely that on the sixth day "the heavens and the earth were finished and all the host of them," Gen. 2, 1, which certainly includes the angels.