In addition to marking a habitual, continuous or progressive occurence of the state or event denoted by the main verb, the marker de can further convey the sense of ingressive/inchoative/inceptive aspect (Van den Berg 2007: 200).
Source: Schumann 1783: 58
Source: Schumann 1783: 39
Source: Schumann 1783: 116
Source: Schumann 1783: 63
Source: Schumann 1781: 62