E.g. Sonny has many qualities worth recognizing and the purpose of this letter is to point out two of these/those qualities.
These/those are the plural forms of this/that and behave in the same way. As a determiner this is used to identify a specific person or thing close at hand or being experienced. As a determiner that refers to the more distant of two things and this refers to, of two things, near to the speaker or to a specific thing previously mentioned.