In this ayaah Allah is telling us a story. The story of a people who were given the book. Allah tells us that they had some sort of relationship with the book they were given. They may have read it beautifully, memorized it, celebrated it etc. but as soon as it came to this book making decisions for them, deciding right and wrong for them, they turned away.
Doing an act of charity is a lot like planting a seed. In order for this seed to mature into a plant from which we may benefit there are certain conditions which have to be met and many things that need to be taken care of.
I am standing on the day of Qiyamah, helplessly looking at the angels gathering and piling my deeds on top of each other in front of me. Allah is there in front of me, on His throne, in all His majesty. The first time I am able to look at my Allah but I am too scared to look up. I am just standing there paralyzed with fear, unable to tear my eyes away from whatever the angels are bringing.
A believer is not the one who will sit in a corner depressed or give up even before the battle starts. Our imaan gives us the confidence to look our enemy in the eye, no matter how big he is and say "Allah is with the patient!"
Selling one's self to please Allah is a very strong expression in itself. But coupled with the word "maradhaat" the meaning is intensified even further. It means that these slaves do not seek just the pleasure of Allah, they seek the extreme pleasure of Allah. They go above and beyond in their desire to please their Master.
So until I find my Judi, I sail in the fragile vessel of my Imaan, in a world full of darkness and confusion, putting all my trust in Allah and saying as Nuh said: In the Name of Allah will be its (moving) course and its (resting) anchorage. [Hud: 41]
We are supposed to recognize our own gifts. We are supposed to discover our own talents, our skills, our strong points. And we are supposed to use these bounties of Allah in the service of His creation.
But in this ayaah Allah is telling us the correct balance between the two extremes. He is telling us His way, His definition of the right path, His definition of "al Birr" - the good deeds.
If there is one word which could describe the heart, it would be "change". How many times have we experienced our feelings, our emotions and our inclinations change. Our desires, our wishes, our passions, everything is in a continuous roller coaster of change.
There are many Ayaat in the Quran that end in the attributes of Allah (Most High). And always there is a connection between the context of the ayaah and the attribute being mentioned. In fact the precise endings of the ayaat (al khawateem) is a linguistic feature of the Quran and a study on its own.