Allah tells us how insignificant and transient this world is, and how it will soon end. All that it
وَإِنَّ الدَّارَ الاٌّخِرَةَ لَهِىَ الْحَيَوَانُ
(Verily, the home of the Hereafter -- that is the life indeed,) means, the true everlasting life that will never end, but will continue forever and ever.
لَوْ كَانُواْ يَعْلَمُونَ
(if they but knew.) means, they would prefer that which will last over that which will pass away. Then Allah says that at times of calamity, the idolators call upon Him alone, with no partner or associate, so why do they not do that all the time
In the preceding verses it was said about the infidels and disbelievers that if they were asked about the creation of the earth and skies, the solar system, the water cycle and its effect on growth of vegetation, they would reply that all this is created and controlled by Allah Ta a1a. They did not believe that any one had any involvement in their creation or control, yet in their worship they associate idols with Allah. The reason for this is أَكْثَرُهُمْ لَا يَعْقِلُونَ (Most of them do not understand - 29:63).
At this point the question arises that, after all, they were not insane but intelligent and sensible people. They performed many important and skillful jobs. Then, how have they lost their balance of mind? The answer to this query is given in the first of the above verses by saying that they are lost in the love of material attractions of the world, which are mortal and would disappear soon. They are totally oblivious of the life hereafter, which would last forever. The life of this world is nothing more than a pastime for amusement and fun, but the real and lasting life is that of Hereafter. وَمَا هَـٰذِهِ الْحَيَاةُ الدُّنْيَا إِلَّا لَهْوٌ وَلَعِبٌ وَإِنَّ الدَّارَ الْآخِرَةَ لَهِيَ الْحَيَوَانُ (And this worldly life is nothing but an amusement and play, and the Last Abode is the real life indeed. - 29:64). Here the word Hayawan is used in the sense of hayah (life) (Qurtubi).
The real reason for a man going astray is that he is so completely engrossed in the glamour and problems of the world that he cannot rise above them and think independently. In order to arrive at the Truth, one has to raise oneself above external and superficial appearances. Most of the people cannot do so, and that is why they do not find the Truth. In the world, time and again, man has experiences which remind him of his helplessness. At that time all his conditioning fall away from him and the real and natural man in him is awakened. But as soon as conditions return again to normal, he becomes as neglectful and arrogant as before. Among these crucial experiences is that of a voyage, which is mentioned in the verse. Man should know that the chance to exercise freedom is given to him during this life for only a few days. After death, he will have to face a completely new world with a completely different set of problems.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.