That is why Saint Thomas, who said in the prologue that he was looking at the image of God in the acting man, begins with the consideration of the ultimate end of human life. In a map of a city, we look at the general plan and then the details. So we begin with the most profound aspiration, moving us to what is ultimate. The concept of finality in man and what it implies The ultimate end is said to be happiness. The final end, within us, is something that is not imposed from without.
Nothing can be the greater source of happiness than our ultimate end.
So Saint Thomas is not searching for an abstract end. The first article asks whether it is appropriate for man to act in pursuit of an end. He responds that acting out of a deliberate choice is typical for man as a rational being. In working toward an end we reflect the image of God. We have many proximate ends, but all are ordered to the ultimate end.