Which is better – devoting oneself to da’wah or seeking knowledge?

Seeking knowledge is better and is preferable, but the seeker of knowledge may call people to Allaah whilst he is also seeking knowledge, but it is not possible to call people to Allaah when one has no knowledge. Allaah says (interpretation of the meaning):

“Say (O Muhammad): ‘This is my way; I invite unto Allaah (i.e. to the Oneness of Allaah — Islamic Monotheism) with sure knowledge…”

[Yoosuf 12:108]

How can there be da’wah with no knowledge? No one ever called anyone to Allaah without having knowledge; whoever calls people without knowledge will not be helped by Allaah.