مَثَلُ الَّذِينَ كَفَرُوا بِرَبِّهِمْ ۖ أَعْمَالُهُمْ كَرَمَادٍ اشْتَدَّتْ بِهِ الرِّيحُ فِي يَوْمٍ عَاصِفٍ
Mathalul-ladheena kafaroo bi-rabbihim, a‘maalahum ka-ramaadini-shtaddat bihir-reeHu fee yawhin ‘aaSifi
The parable of those who disbelieve in their Lord: their actions are like ashes on which the wind blows hard on a stormy day.Surat Ibrahim (No. 14), Aayat 18
Actions in Islam carry value based on their intentions. A small action done for the sake of Allah carries great reward and is huge in the eyes of Allah, for Allah looks at the heart that does the action, not the action itself. What beautifies and magnifies actions is the love for Allah that lies behind them. The Holy Prophet (s) has said; Make your heart sincere and a little of action will be sufficient for you.
Love of Allah is the thread that binds actions of a believer together, and makes it into a solid foundation of good deeds. Without this binding thread actions carry no weight and are scattered around. This is the truth referred to in the verse above, where Allah says the example of such deeds (that are not done for the sake of Allah) are like ashes, scattered around by strong wind.
Ayatullah Nasir Makarim Shirazi gives the following points under this verse;
1) Ash is the remains of fire, and has no benefit in itself. Nothing grows from it. A small pot of soil can have plants growing in it, but nothing can emerge from ash.
2) The particles of ash are not bound together and can easily be blown away separately. This is very different from believers whose actions are for Allah, and are bound together by their faith.
3) Once the particles of ash are blown away, nothing can bring them together again. They lose their identity and cannot be discerned. Such is the weakness of actions done without faith.
4) The wind that has plays such a useful role in Nature does not have the same effect on ash. Instead of benefitting from the wind, it is blown away and becomes useless.
A sincere intention is everything. Work hard to purify your intentions so that your actions carry value. That is actually harder than the action itself.
Sources:
Tafsir Namune, Aytaullah Nasir Makarim Shirazi (ed).
Mizanul Hikmah, Muhammad al-Ray Shahree