Examples are useful to understand and realize the true sense or meaning of preaching.
Here (in BG 2.67), the example of wind carries out ship on the sea has following preaching sense:
Here the main goal/objective of man is to know and realize the true self. But indriya/senses can divert the main goal (of realizing true self) through controlling mind (when followed/focused on indriya/senses) in experiencing the sense-objects.
Now, let's consider the example given for preaching this:
The main objective/goal of man who is running ship is to reach at the destination by directing ship towards the goal but wind can divert the direction and the ship controlled by wind instead of man can never reach the destination as it roves.
So, as wind carries out (control and divert) the ship, similarly indirya/sense (on which mind is followed/focused) carries out (diverts, roves) the wisom/intellect of man from the spirituality.
Let me quote Adi Shankaracharya & Ramanujacharya's commentary on BG 2.67 which are useful and reliable interpretation to get the true sense of what is being preached or explained with the help of wind-ship example (quoted from Gita Supersite):
English Translation Of Sri Shankaracharya's Sanskrit Commentary By Swami Gambirananda
2.67 Hi, for; yat manah, the mind which; anu-vidhiyate, follows in the wake of; caratam, the wandering; indriyani, senses that are tending towards their respective objects; tat, that, the mind engaged in thinking [Perceiving objects like sound etc. in their respective varieties.] of the objects of the senses; harati, carries away, destroys; asya, his, the sannyasin's; prajnam, wisdom born from the discrimination between the Self and the not-Self. How? Iva, like; vayuh, the wind; diverting a navam, boat; ambhasi, on the waters. As wind, by diverting a boat on the waters from its intended course, drives it along a wrong course, similarly the mind, by diverting the wisdom from the pursuit of the Self, makes it engage in objects. After having stated variously the reasons for the idea conveyed through the verse, 'For, O son of Kunti,' etc. (60), and having established that very idea, the Lord concludes thus:
English Translation of Ramanuja's Sanskrit Commentary By Swami Adidevananda
2.67 That mind, which is allowed by a person to be submissive to, i.e., allowed to go after the senses which go on operating, i.e., experiencing sense-objects, such a mind loses its inclination towards the pure self. The meaning is that it gets inclined towards sense-objects. Just as a contrary wind forcibly carries away a ship moving on the waters, in the name manner wisdon also is carried away from such a mind. [The idea is that the pursuit of sense pleasures dulls one's spiritual inclination, and the mind ultimately succumbs to them unresisting.]
You can also find the various commentaries on bhagavad-gita.us
Here example is analogous as follows:
- Ship (by means of which man can reach at the destination) -:- Intellect or Wisdom (by means of which man can enrich the spiritual level to attain the true self)
- Wind (which can divert the ship) -:- Indriya (which can be cause of diversion of mind from spiritual inclination)
How the example is not trivial or silly:
You can imagine how it is unexpected or dangerous when a man loss controls on ship if wind diverts the direction and ship can't reach at the destination. Similarly it is as unexpected/dangerous as can be imagined from above example for one who is on spiritual journey.
Thus, the purpose of example is to get the idea how indriya/senses can interrupt and divert the spiritual goal of pursuing the self.