Tafsir of Al-Isra 17:66

Ships are a Sign of the Mercy of Allah Allah says;

ربكم الذي يزجي لكم الفلك في البحر لتبتغوا من فضله

Your Lord is He Who drives the ship for you through the sea, in order that you may seek of His bounty. Allah tells us of His kindness towards His servants by subjugating for them ships on the sea. He makes it easy for them to use ships to serve their interests, seeking His bounty through trade between one region and another. He says:

إنه كان بكم رحيما

Truly, He is ever Most Merciful towards you. meaning, He does this for you out of His grace and mercy towards you