لِنَجْعَلَهَا لَكُمْ تَذْكِرَةً ...

That We might make it an admonition for you,

The pronoun "it'' here refers to the species of the object (ships) due to the general meaning alluding to this. Thus, the meaning is, `We caused its type of creation (ships) to remain (in the earth) for you, so that you ride upon the currents of the water in the seas. '

This is as Allah says,

وَجَعَلَ لَكُمْ مِّنَ الْفُلْكِ وَالاٌّنْعَـمِ مَا تَرْكَبُونَلِتَسْتَوُواْ عَلَى ظُهُورِهِ ثُمَّ تَذْكُرُواْ نِعْمَةَ رَبِّكُمْ إِذَا اسْتَوَيْتُمْ عَلَيْهِ

and has appointed for you ships and cattle on which you ride; In order that you may mount on their backs, and then may remember the favor of your Lord when you mount thereon. (43:12,13)

And Allah said,

وَءَايَةٌ لَّهُمْ أَنَّا حَمَلْنَا ذُرِّيَّتَهُمْ فِى الْفُلْكِ الْمَشْحُونِ

وَخَلَقْنَا لَهُمْ مِّن مِّثْلِهِ مَا يَرْكَبُونَ

And an Ayah for them is that We bore their offspring in the laden ship. And We have created for them of the like thereunto, on which they ride. (36:41,42)

Qatadah said,

"Allah caused this ship to remain until the first people of this Ummah saw it.''

However, the first view (that it refers to all ships in general) is the most apparent.

Allah continues saying,

... وَتَعِيَهَا أُذُنٌ وَاعِيَةٌ ﴿١٢﴾

and that it might be retained by the retaining ears.

meaning, that a receptive ear may understand and reflect upon this bounty.

Ibn `Abbas said,

"This means an ear that is retentive and hearing.''

Qatadah said, أُذُنٌ وَاعِيَةٌ (by the retaining ears), means:

"An ear that Allah gives intelligence, so it benefits by what it hears from Allah's Book.''

Ad-Dahhak said, وَتَعِيَهَا أُذُنٌ وَاعِيَةٌ (and that it might be retained by the retaining ears). means,

"An ear that hears it and retains it, meaning the person who has sound hearing, and correct intellect.''

And this is general concerning everyone who understands and retains.