They say that Halloween is one of the most unholy nights of the year. Well, it's up to you to change that with a Jesus Halloween costume. It may seen a little contradictory to you, but it doesn't have to be.
First, grow out your hair and beard. You're going to have to start early, planning months ahead of time if you're going to rely on your natural hair. Alternatively, you could also just wear a wig and a fake beard if you can't commit for so long to a Halloween costume.
Of course, nobody can say for sure what Jesus wore back in the day, but it probably wasn't a T-shirt and jeans. Get some white fabric from the fabric store and make yourself a robe. You can also go to a party store and buy a pre-made Jesus costume - there are tons of them out there. Many of them even come with a fake beard and a wig.
You have to wear sandals if you're going to be Jesus. Look around the shoe store and try to find a brown, classic pair of shoes that is somewhat reminiscent of the time period.
You might want to add something like a staff or a basket with a loaf of bread and a couple of fish to your costume. This helps make it seem more authentic. If the accessory references a Bible story, even better. It may not be Christmas, but it's never too early for having fun with Jesus. Try a Jesus costume this Halloween and bless everyone at the party with your holy presence.