The answer from God’s word:
… first, He is able to open up a new age; second, He is able to supply the life of man and show man the way to follow. This is sufficient to establish that He is God Himself. At the very least, the work He does can fully represent the Spirit of God, and from such work it can be seen that the Spirit of God is within Him. As the work done by the incarnate God was mainly to usher in a new age, lead new work, and open up new circumstances, these few conditions alone are sufficient to establish that He is God Himself. …
from “The Difference Between the Ministry of the Incarnate God and the Duty of Man” in The Word Appears in the Flesh
To study such a thing is not difficult, but requires each of us to know this truth: He who is God’s incarnation shall hold the substance of God, and He who is God’s incarnation shall hold the expression of God. Since God becomes flesh, He shall bring forth the work He must do, and since God becomes flesh, He shall express what He is, and shall be able to bring the truth to man, bestow life upon man, and show man the way. Flesh that does not contain the substance of God is surely not the incarnate God; of this there is no doubt. To investigate whether it is God’s incarnate flesh, man must determine this from the disposition He expresses and the words He speaks. Which is to say, whether or not it is God’s incarnate flesh, and whether or not it is the true way, must be judged from His substance. And so, in determining[a] whether it is the flesh of God incarnate, the key is to pay attention to His substance (His work, His words, His disposition, and many more), rather than external appearance. If man sees only His external appearance, and overlooks His substance, then that shows the ignorance and naivety of man. External appearance does not determine substance; what’s more, the work of God has never conformed with the conceptions of man. Did not the outward appearance of Jesus conflict with the conceptions of man? Were not His appearance and dress unable to provide any clues as to His true identity? Was not the reason why the earliest Pharisees opposed Jesus because they merely looked at His external appearance, and did not take to heart the words that He spoke? It is My hope that the brothers and sisters who seek the appearance of God will not repeat the tragedy of history. You must not become the Pharisees of modern times and nail God to the cross again. You should carefully consider how to welcome the return of God, and should have a clear mind of how to be someone who submits to the truth. This is the responsibility of everyone who is waiting for Jesus to return with the clouds.
from Preface to The Word Appears in the Flesh
The work done at present has pushed forward the work of the Age of Grace; that is, the work in the entire six-thousand-year management plan has moved forward. Though the Age of Grace has ended, the work of God has progressed further. Why do I say time and again that this stage of work builds upon the Age of Grace and the Age of Law? This means that the work of this day is a continuation of the work done in the Age of Grace and an uplifting of that done in the Age of Law. The three stages are closely interconnected and linked one to the next. Why do I also say that this stage of work builds on that done by Jesus? If this stage did not build on the work done by Jesus, then in this stage the crucifixion, the work of redemption done previously, would still need to be carried out. This would be meaningless. Therefore, it is not that the work has completely finished, but that the age has moved forward, and the work has become even higher than before. It could be said that this stage of work is built on the foundation of the Age of Law and the rock of the work of Jesus. The work is built stage by stage, and this stage is not a new beginning. Only the combination of the three stages of work can be deemed the six-thousand-year management plan. This stage is done on the foundation of the work of the Age of Grace. If these two stages of work are unrelated, why is there no crucifixion in this stage? Why do I not bear the sins of man? I do not come through the conception by the Holy Spirit nor will I be crucified to bear the sins of man. Rather, I am here to directly chastise man. If I did not chastise man following the crucifixion, and now I do not come through the conception by the Holy Spirit, then I would not be qualified to chastise man. It is precisely because I am one with Jesus that I come directly to chastise and judge man. This stage of work builds entirely on the previous stage. This is why only such work can bring man to salvation stage by stage. Jesus and I come from the same Spirit. Though Our fleshes have no relationship, Our Spirits are one; though what We do and the work We bear are not the same, We are alike in essence; Our fleshes take different forms, and this is because of the change in era and the need of Our work; Our ministries are not alike, so the work We bring forth and the disposition We reveal to man are also different. That is why what man sees and receives this day is unlike that of the past; this is so because of the change in era. Though the gender and form of Their fleshes are different, and though They were not born of the same family, much less in the same time period, Their Spirits are one. Though Their fleshes share no blood or physical relationship in any way, this does not deny that They are the incarnate fleshes of God in two different time periods. It is an undeniable truth that They are the incarnate fleshes of God, though They do not share the same bloodline or a common human language (one was a male who spoke the language of the Jews and the other is a female who speaks only Chinese). It is for these reasons that They do the work They ought in different countries, and in different time periods as well. Despite the fact that They are the same Spirit, possessed of the same essence, there are no absolute similarities at all between the outward shells of Their fleshes. They merely share the same humanity, but the appearance and birth of Their fleshes are not alike. These have no impact on Their respective work or the knowledge that man has of Them, for, after all, They are the same Spirit and none can separate Them. Though They are not related by blood, Their entire beings are directed by Their Spirits, so that They undertake different work in different time periods, with Their fleshes not sharing a bloodline. Similarly, the Spirit of Jehovah is not the father of the Spirit of Jesus, much as the Spirit of Jesus is not the son of the Spirit of Jehovah. They are the same Spirit. Just like the incarnate God of this day and Jesus. Though They are not related by blood, They are one; this is because Their Spirits are one.
from “The Two Incarnations Complete the Significance of the Incarnation” in The Word Appears in the Flesh
a. The original text reads “as for.”