The plain meaning of the text is that a Nazirite is warned not to consume wine seeing that anyone who allows his desire for wine and alcoholic drink to determine his actions will give in to other temptations involving matters which are forbidden even in moderate quantities, to lead him astray. The reason the Nazir has been commanded to grow his hair long is that long hair causes people to worry, and the Torah wants the Nazir to worry about not breaking the constraints of his vow. When he looks dishevelled due to his unruly hair he will also abstain from other activities which reflect dishonor upon man. Hair is perceived as the remnant and excess of “smoldering“ physical forces that the body emits.
The expression יפליא in our verse refers to the Nazirite doing something פלא, wonderfully different. Whereas all the world indulge their senses, the Nazirite has decided to not only repress his evil urge but to fortify his resolution by making a vow to abstain from wine, the prime cause of stimulating such temptations.
The expression נזיר occurs first in connection with the Priests being commanded not to touch the holies of the Children of Israel when in a state of ritual impurity (Leviticus 22:2). In that instance the word means: “to separate, to withdraw.”
Another instance where we have encountered this expression is Exodus 29:6 in connection with Aaron’s headgear. It is described as נזר הקדש — a sort of crown which set Aaron apart from the other Priests. Crowns are worn by Royalty, i.e. people in authority. A Nazir is so called because he is like a king in that he rules over his desires, unlike the majority of mankind who are slaves to temptation.