‘The Tyger’ contains a series of rhetorical questions, which we understand to be about the nature of the creator of the Tyger. The first questions are given in conventional English syntax:
What immortal hand or eye,
Could frame thy fearful symmetry?
In what distant deeps or skies
Burnt the fire of thine eyes?
On what wings dare he aspire?
But then as the poem progresses, words begin to be omitted. At first it is easy to fill in the gaps:
What [is] the hand, [that] dare seize the fire?
At this stage this is no more than conventional poetic elision, but the omissions give the impression of haste, as if the message is so urgent that there is no time to spell out the details, and so important that syntax can be abandoned. The omissions increase in frequency as the poem goes on, giving an impression of acceleration:
And when thy heart began to beat,
What dread hand […]? & what dread feet […]?
What […] the hammer […]? what […] the chain […],
In what furnace was thy brain […]?
What […] the anvil […]?
Here it is not quite so easy to fill the gaps. We must stretch our imagination to figure out what the poet must have intended the questions to be. We can tell from the fragments that we are presented with, that the creator is being personified as a blacksmith, so that the questions must be along these lines:
What dread hand [could wield the hammer]? & what dread feet [could pump the bellows]?
What [is] the hammer [that beat thee]? what [is] the chain [that lifted thee],
In what furnace was thy brain [forged]?
What [is] the anvil [on which thou wert beaten]?
After this dramatic and compressed climax the poem returns to conventional syntax.
You are not obliged to read the poem in this way, but if you do, then there is no difficulty with the presence of the word “the”: it is used in its normal sense, but stands out because so many other words have been elided.