2. The element of persistence is implied even in...
a. The present progressive tense of the verbs for "ask", "seek", and "knock" (literally, "keep on asking", "keep on seeking", and "keep on knocking"
b. The progressive relation between the words:
1) One normally starts out by "asking"
2) As they learn more, they begin "seeking"
3) As they arrive close to their destination, they start "knocking"