I have an LG 4K UHD Smart TV. I want to wirelessly cast my screen to the tv from a Macbook Pro without using any streaming device. Please help.

That is not possible

You need either a hook up with an HDMI cable (Not wireless)

or a device like Apple TV or Chromecast to communicate the images from the Mac and render it on the TV (not without device)

There is an app called Firestream that will connect to DLNA enabled smart tv's and will stream certain files(mp3's, mp4's, mkv's) wirelessly through your wi-fi network. It is available through the App Store.

if lg or the likes make an app which can speak with their tv yes, otherwise you need a cable or an appletv or maybe a cromecast or some miracast(if they support such a thing) and connect them to the tv by passing the smart part of the tv really.