بسم الله الرحمن الرحيم
If He willed, He could still the wind, and they would remain motionless on its surface. Indeed in that are signs for everyone patient and grateful.
[Surat Ash-Shuraa, 42:33]
Allah tells us that another sign of His great power and dominion is the fact that He has subjugated the sea so that ships may sail in it by His command, so they sail in the sea like mountains. This was the view of Mujahid, Al-Hasan, As-Suddi and Ad-Dahhak. In other words, these ships on the sea are like mountains on land.
إِن يَشَأْ يُسْكِنِ الرِّيحَ
(If He wills, He causes the wind to cease) means, the winds that cause the ships to travel on the sea. If He willed, He could cause the winds to cease, then the ships would not move and would remain still, neither coming nor going, staying where they are on the surface of the water.
إِنَّ فِى ذلِكَ لآيَـتٍ لِّكُلِّ صَبَّارٍ
(Verily, in this are signs for every one patient) means, who is patient in the face of adversity
(and grateful.) means, in the fact that Allah has subjugated the sea and He sends as much wind as they need in order to travel, there are signs of His blessings to His creation for everyone who is patient, i.e., at times of difficulty, and grateful, i.e., at times of ease.
Source: Tafseer ibn Katheer