You should not have wondered because I have declared it was needed for you all to have been begotten from above.
Jhn 3:7 Marvel not that I said unto thee, Ye must be born again.
Interesting and Hidden Aspects:
From the translation, you might think that this phrase would parallel the construction of Jhn 3:3, the statement to which Christ is referring. However, it actually is quite different.
One thing that is the same is the tense of the "being born" verb. It is in the aorist tense, which is usually translated in English as the past. It indicates something that happens at a particular point in time. Most the verbs here are aorist, even when they don't appear that way in English: "marvel", "said," and "be born." The verb "must" is in the imperfect tense, which indicates an action begun in the past. Since we know that Christ made this statement in the past, we can assume that everything else is past as well. This means that verse this doesn't refer to a future baptism (a possible interpretation of the "birth of water" of Jhn 3:5 ) but past births (plural, see below).
Now it gets more interesting. The Jhn 3:3 "be born" verb was made in the third person singular. It referred to a single person having been born or begotten "from above," and therefore, it could have referred to Christ. Here, however, the statement is made about the second person, plural, "for you all."
The term translated as "you must" is a 3rd singular statement. This is the usual form of this verb, which is normally translated as "it was needed" or "there was a need".
And, of course, the final word translated as "again" (anothen) actually means "from above." It is not the word translated as again everywhere else in the NT (palin).
So, Christ is not repeating what he said. He is clarifying what he meant. He meant that everyone must be at some time born of the spirit as well of the flesh. That people have a "from above" birth just like they do a physical birth. So it is a restatement of Jhn 3:6 That which is born of the flesh is flesh...
Since people are both physical and spiritual we have two births. One here on earth, apparently the water birth, and another from above, the spiritual birth, that of the wind or breath. This is consistent with Christ's use of water as a symbol for life. As we go through it, this looks less and less like a promotion of baptism, as it is usually taken. It is a ontological statement, referring to the nature of being and becoming.
μὴ "Not" is from mê (me), which is the negative used in prohibitions and expressions of doubt meaning "not" and "no." As οὐ (ou) negates fact and statement; μή rejects, οὐ denies; μή is relative, οὐ absolute; μή subjective,οὐ objective.
ὅτι "That" is from hoti (hoti), which introduces a statement of fact "with regard to the fact that", "seeing that," and acts as a causal adverb meaning "for what", "because", "since," and "wherefore."
εἶπόν (1st sg aor ind act) "I said" is from eipon (eipon), which means "to speak", "to say", "to recite", "to address", "to mention", "to name", "to proclaim", "to plead", "to promise," and "to offer."
γεννηθῆναι (aor inf pass) "Be born" is from gennaô (gennao), which means "to beget", "to bring forth", "to produce from oneself", "to create," and "to engender." This is the causal form of gignomai, which is translated as "done" in the NT, but which comes closer in meaning to "become."
ἄνωθεν "Again" is from anothen, which means "from above", "from on high," [in a narrative] "from the beginning" or "from further back", "higher", "more universal," [NT translation] "over again", "anew," and "afresh."