Angels will not stop believers sinning either. The angel in the wilderness did not stop the people of Israel sinning. When he does return, the angels will come with him. The angels will be involved in bringing people together for judgement. At that time, the believers will be made like the angels.
Angels are messengers.
They can also guide, protect, deliver and destroy. They help those who are true believers, but do not stop people committing sin. They are usually not seen. When they were seen they appeared in many different forms. They cannot sin, do not marry, and never die.