Do good. — The last two verses have occasioned much controversy. They do not fit in well with the theory of Davidic authorship, Theodoret long ago saying that they better suited the exiles in Babylon. They seem at first sight to contradict what has just been asserted of sacrifice. On both grounds they have been regarded as a liturgical addition, such as doubtless the compiler made, without any sense of infringement of the rights of authorship. On the other hand, it is not only these two verses which harmonise with the feelings of the restored exiles, but the whole psalm, and the contradiction in regard to the worth of sacrifices is only apparent. While vindicating spiritual religion, the psalmist no more abrogates ceremonies than the prophets do. As soon as their performance is possible they will be resumed.
Related Commentaries of Psalms 51:18
Psalms 51:18
18 Do good in thy good pleasure unto Zion: build thou the walls of Jerusalem.