Ki in Dragon Ball is basically the life force of every character that can be used to manipulate a variety of techniques. As such, there is normal Ki which is used by ordinary beings and then there is God Ki that is used by divine beings.
Goku, the primary protagonist of the series, has reached multiple power levels, including Super Saiyan Blue and even Ultra Instinct. These are techniques that use God Ki, but there is a difference between using it and attaining True God Ki permanently. Thus, in this article, a discussion has been made on why Goku will never attain it.
However, it is important to remember that the discussion is based on speculation, since in Dragon Ball almost anything can happen at any moment. Apart from that, logic and reasoning are often tough to come by since there are multiple plot holes present throughout the series.
A brief discussion on why it is impossible for Goku to obtain True God Ki in Dragon Ball
Goku in Dragon Ball has already transcended to levels that can surpass a God. His Super Saiyan Blue is something that can rival a God, while his Ultra Instinct is a level that even Gods find difficult to achieve.
Despite that, Goku attaining True God Ki while in base form will be impossible. The short answer to that is because it will sort of beat the entire purpose of the show in general, making all the previous forms useless.
There is a massive difference between using God Ki to reach a certain level and attaining it completely while in base form. Someone like Beerus has True God Ki even when he is in a normal state. In other words, Beerus does not have to train day in and day out to master it.
However, Goku needs to train continuously to ensure that he can keep forms like Super Saiyan Blue and techniques like Ultra Instinct in control. Using God Ki is no easy task as it requires extreme concentration and puts immense strain on the body. Apart from that, transforming into Super Saiyan Blue requires a Super Saiyan 1 transformation before mixing the God Ki.
Goku partially obtained God Ki during his transformation to Super Sayian God (Red form), through a ritual. Vegeta, on the other hand, obtained it through intense training that Whis put him through.
However, this God Ki is only used to transform into Super Saiyan Blue or beyond. Unfortunately, the God Ki that they obtained is something that can be extracted through immense concentration. It is not something that has replaced their Normal Ki.
Therefore, they are not Gods, despite using techniques that can rival a God. However, if Goku was able to obtain True God Ki by some means that replaced his original Ki, then he would be able to do things that Beerus can as well.
Goku could be sleeping in peace while tapping his finger to destroy half of the universe. That is the difference True God Ki can make and the only way to obtain it completely and replace the Normal Ki is through divine blessing.
The problem with this is that, if Goku does fully obtain True God Ki, he will become sort of like One Punch Man, and the concept of training to obtain power and reach new heights will be defeated. Dragon Ball, at its core, shows Goku's struggles through which he reaches impossible heights.
However, once he fully obtains True God Ki, that ceiling will be broken and he will have nowhere else to reach. He can still obtain things like Ultra Instinct or more, but he will never truly become a God.
This is because, at the end of the day, it is vital to remember that Ultra Instinct in Dragon Ball Super is a technique that can be obtained while Goku is in base form. Hence, it does not require God Ki but can be enhanced using the same.