Question

why voltmeter has high resistance

Answer 1

On the other hand, a voltmetermeasures the voltage difference between two different points (say, on different sides of a resistor), but it should not change the amount of current going through the element between those two points. So, it should have very high resistance so that it doesn't "draw" current through it.

Answer 2

volt meter has high resistance because so that it will draw negligible current when placed in parallel with a resistor