With every breath you take, a thanksgiving is incumbent upon you, indeed, a thousand thanks or more. The lowest level of gratitude is to see that the blessing comes from Allah irrespective of the cause for it, and without the heart being attached to that cause. It consists of being satisfied with what is given; it means not disobeying Him with regard to His blessing, or opposing Him in any of His commands and prohibitions because of His blessing.
Be a grateful bondsman to Allah in every way, and you will find that Allah is a generous Lord in every way. If there were a way of worshipping Allah for His sincerest bondsman to follow more excellent than giving thanks at every instance, He would have ascribed to them the name of this worship above the rest of creation. Since there is no form of worship better than that, He has singled out this kind of worship from other kinds of worship, and has singled out those who practise this kind of worship, saying,
وَقَلِيلٌ مِّنْ عِبَادِيَ الشَّكُورُ
Very few of my servants are grateful. (34:13)
Complete thankfulness is to sincerely repent your inability to convey the least amount of gratitude, and expressing this by means of your sincere glorification of Allah. This is because fitting thanks is itself a blessing bestowed upon the bondsman for which he must also give thanks; it is of greater merit and of a higher state than the original blessing which caused him to respond with thanks in the first place. Therefore, every time one gives thanks one is obliged to give yet greater thanks, and so on ad infinitum, and this while absorbed in His blessings and unable to achieve the ultimate state of gratitude. For how can the bondsman match with gratitude the blessings of Allah, and when will he match his own action with Allah's while all along the bondsman is weak and has no power whatsoever, except from Allah?
Allah is not in need of the obedience of His bondsmen, for He has the power to increase blessings forever. Therefore be a grateful bondsman to Allah, and in this manner you will see wonders.
--From Imam Sadiq (as) in Lantern of the Path.