Rumour has it, these ancient gates are residual technology from a long extinct civilization. Perhaps a kind of altar. It is thought they were used to equalise the balance of power amongst inhabitants by temporarily revoking access to weapons or abilities.
When standing on the gate, you can see what it will affect:
Removes the blaster. Perhaps a short-range weapon could slip through unnoticed?
Removes the jet-pack. Only a very small hop is possible without it.
Removes the shield. Proceed with caution!
Maxwell is unable to trick the ancient gates into allowing the shield or jet-pack through, however, after collecting the Laser Blade, it is possible to remain armed after the gate removes the blaster.
While most gates are separate from each other, there are single gates that combine the functionality of all three where Maxwell would need to time the activation of the gate to choose which equipment to forgo.