- The large calligraphy says 髙（高）明⿰酉卩（配）天
- The seal says 𢿩（敬）璧
「高明配天」 is a short segment from the Doctrine of the Mean. The entire line that this segment is found in is
...one's learning as expansive as the land on this earth, one's achievements as noble and lofty as the blue sky, lasting through to eternity...
The seal 「敬璧」 is part of the name of the artist (as given on the smaller calligraphy on the left).
Generally, if you find something that kind of looks like seal script but feels somewhat off (e.g. you can't identify some components), you can assume that it's some kind of pre-Qin writing style. I would classify the large calligraphy as being inspired by oracle bone script and the seal as being inspired by inscriptions from around the Spring and Autumn period.
We can have a go at explaining the character shapes below...
The closest shape to the first character in the large calligraphy is 「髙」, which we normally write nowadays as 「高」. 「高」 (high/lofty/tall) is made up of semantic 「京」 (picture of a tall watchtower/pavilion) and a distinguishing mark 「口」 whose function is to distinguish the word represented by 「高」 from the word represented by 「京」.
The third character in the large calligraphy transcribed into regular script is
which was originally made up of a kneeling person 「卩」 next to an alcohol vessel 「酉」. The original meaning was an abstraction of people jointly kneeling or prostrating at a ritual (and wine was often an offering in these rituals), and the joint ritual meaning was semantically extended to join, pair, match.
「卩」 was then corrupted into 「己」.
The closest shape to the first character in the seal is 「𢿩」, and this is normally written nowadays as 「敬」. The character 「敬」 (Zhengzhang OC: /*kreŋs/, respect) comes from semantic 「攵・攴」 (hand holding a hitting weapon) and phonetic 「茍」 (/*kɯɡ/). The shape in the seal comes from a corruption of the
part of 「茍」 into 「羌」, and this corruption is not inherited in the modern form 「敬」.
Note: the proportions have been distorted slightly in the seal.
This should be recognisable from the small calligraphy on the left, if not for the distorted proportions.