Of course, as the Talmud and Christian commentary make clear, things may be more complicated than they first appear, but basically what is required is following God's will. Of course, this begs the question of what God's will is, and the basis on which we know this. And then, of course, we have the problem of properly characterizing what we mean by these concepts. For Kant, morality is fundamentally characterized in terms of the intention with which one acts. One can act out of compassion and one can act on the basis of inclination, but neither of these would constitute acting morally.
Morality involves acting with the pure intention of performing one's duty.
In other words, act on a rule that would apply to everybody, including yourself. Some have suggested that Kant's idea resembles the Golden Rule, but the Golden Rule appeals to individual sensibility in relation to what one would want for oneself. Kant is appealing to the rational element of willing, that one should act in a way that does not logically allow one to make an exception for oneself. In other words a will at odds with itself is not a pure will or one aiming purely to act with the intention of performing one's duty. Another major aspect of Kant's thought is that persons are always to be treated as ends, never as means.