The voltmeter has high resistance because the resistors are connected in parallel between two points, and if the resistance is not high, an electric current will pass, the reading will change, and an error will occur.
The voltmeter is built with a very high internal resistance, because it measures the potential difference between the two points of the circuit, and the voltmeter must not change the measured current, if its resistance is low, the current will pass through it, and it will give an incorrect result, in other words, the high resistance of the voltmeter does not allow the current The electrode passes through it and thus gives the correct reading