1)-sink the input impedance of the powered chip
—-many chips with input pins will have non-zero voltages when the chip is powered on. If your input voltage is below the chip’s input impedance (which will vary with voltage VCC/VDD to the chip), you input isn’t going to signal the pin. If the input pin is grounded, it will read zero volts in the absence of input current. Any small voltage will switch the pin state from low to high.

2)-sink the current from your input.
—-your input current has one goal in life – go to ground.
—-if it can’t get it ground, something will get hot, fast, then go sizzle, sizzle and finally pop (maybe with a little smoke, followed by a moment of regret).
—-A pull down resistor provides that path to ground while retaining the signal.

Remember, it is voltage, not current that your IC uses for a signal. Excess current >25mA is what makes your ic hot.

As for the pull up resistor explanation…the resistance of a loop in a circuit does not ‘hold’ current, it the amount of current flowing. The current at any point in a single loop of a series circuit is the same. What the pull up resistor does do is stabilize the voltage at the pin, which is acting as an effective ground for VCC. Pin 1 should be at VDD if nothing is connected to it. With the Pull-Up connected, fluctuations in the Pin 1 voltage would be damped by the ration of the input impedance and the value of R1. The IC’s input impedance is usually on the order of 230 ohms.