Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(And when harm) hardship and tribulation (toucheth you upon the sea, all unto whom ye cry (for succour) fail) you leave the idols which you worship, and you do not ask them to save you, (save Him (alone)) you only ask Allah to save you, (but when He bringeth you safe to land, ye turn away) from thanking Him and declaring His divine Oneness, (for man) the disbelieving man (was ever thankless) He denies the bounties of Allah.
And when distress, difficulty, befalls you at sea, [such as] fear of drowning, those whom you [are wont to] invoke are no longer present, [those whom] you [are wont to] worship of gods [are no longer present], and so you do not call on them — except Him, exalted be He, for on Him alone you do call, because you are suffering a distress which only He can remove. But when He delivers you, from drowning and brings you, to land, you are rejective, of [God’s] Oneness, for man is ever ungrateful, [ever] denying [God’s] graces.
(And when harm touches you upon the sea, those that you call upon vanish from you except Him.) meaning, everything they worship besides Allah disappears from their hearts and minds. Similar happened to `Ikrimah bin Abi Jahl when he fled from the Messenger of Allah after the conquest of Makkah, and headed for Ethiopia. He set out across the sea to go to Ethiopia, but a stormy wind arose. The people said to one another: "None can save you except Allah Alone.'' `Ikrimah said to himself, "By Allah if none can benefit on the sea except Allah then no doubt none can benefit on land except Allah. `O Allah! I promise You that if You bring me safely out of this, I will go and put my hand in the hand of Muhammad and surely, I will find him full of pity, kindness and mercy.''' They came out of it safely and were delivered from the sea. Then `Ikrimah went to the Messenger of Allah, and declared his Islam, and he became a good Muslim, may Allah be pleased with him.
فَلَمَّا نَجَّـكُمْ إِلَى الْبَرِّ أَعْرَضْتُمْ
(But when He brings you safe to land, you turn away.) means, you forget what you remembered of Divine Oneness (Tawhid) when you were on the sea, and you turn away from calling on Him Alone with no partner or associate.
وَكَانَ الإِنْسَـنُ كَفُورًا
(And man is ever ungrateful.) means, by nature he forgets and denies His blessings, except for those whom Allah protects.
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
This passage (vv. 66-72) is closely connected with the previous one. It tells man that if he wants to protect himself from the allurements, temptations and false promises of Satan who has been his avowed enemy from the day of his creation, he should recognize his real Lord and be steadfast in His obedience. Satan intends to prove that man is not worthy of the honor with which Allah has blessed him. Therefore if he follows any other way he cannot escape the snares of Satan.
In this passage, arguments of Tauhid have been put forward in order to make man steadfast in his Faith and refrain from shirk.
That is, "Try to avail of the economic, social, educational and intellectual benefits which are provided by the sea voyages."
That is, "This is a proof of the fact that your real nature knows no other Lord than Allah, and you feel in the depths of your hearts that He alone possesses the real power of every gain or loss. Had it not been so, man would never have invoked Allah at the time when he realized that no other helper could remove his misfortune."
And when distress befalls you at sea, those whom you are wont to invoke are no longer present, except Him…That is, those other than Him from whom you ask relief. Then [eventually] you give up all dependency on your own power (ḥawl) and strength (quwwa) and recognise His power and His strength. This verse is a refutation of the Qadarīs, who claim to have ability for themselves without [the need for] God, Exalted is He. God, Exalted is He, has said, Do you feel secure that He will not cause a slope of land to engulf you, or unleash upon you a storm of pebbles? [17:68] And He said, or unleash upon you a shattering gale to drown you [17:69]. So, if they really have ability (istiṭāʿa), let them repel the punishment from themselves.His words, Exalted is He: