In William Blake's "The Tyger", the creator is described in terms of a blacksmith, modelling nature and giving form to a sensuous yet dangerous and potentially evil creature.
On the other hand, in "The Lamb", the creator is described as meek and benevolent, having created the Lamb with its soft wooly clothing and soft voice.
The two poems reflect on the duality of God and religion, and the existence of good and evil. The same God that is merciful, and benevolent is equally capable of creating a creature like the tiger, and tolerate evil in the world as part of his creation. The point is that each creation bears a reflection of its creator.
The speaker in "The Lamb" is innocent enough to only contemplate the good deeds of God in this world, and thus, he answers the question "who make thee" In contrast, the speaker in "The Tyger" is experienced and confronted with the realization of the complexity of God's creation, thus leaving the question unanswered.