I understand it metaphorical words.
As we have already seen, according to many Hadithes, Day of Resurrection is, the Day of Manifestation of the Qaim.
Seeing it in this light, therefore everyone's belief or disbelief is tested by their belief or disbelief in the Qaim at the time of His Manifestation.
Meaning, if a man says, i believe in God, Muhammad and the Quran, but he does not recognize the Qaim when He is manifested, His belief is not accepted, and will be counted as a disbeliever. Thus, their very own response to the call of the Qaim, is, in the sight of God, testimony of their their disbelief against themselves!
This is expressed metaphorically as "their skin and body parts testifies against themselves", because even if they claim and consider themselves as believers in God and Quran, but they have rejected the Qaim with all their beings, this is a testimony to their disbelief in the sight of God.
Now consider this verse:
هَلۡ یَنظُرُونَ إِلَّاۤ أَن تَأۡتِیَهُمُ ٱلۡمَلَـٰۤىِٕكَةُ أَوۡ یَأۡتِیَ رَبُّكَ أَوۡ یَأۡتِیَ بَعۡضُ ءَایَـٰتِ رَبِّكَۗ یَوۡمَ یَأۡتِی بَعۡضُ ءَایَـٰتِ رَبِّكَ لَا یَنفَعُ نَفۡسًا إِیمَـٰنُهَا لَمۡ تَكُنۡ ءَامَنَتۡ مِن قَبۡلُ أَوۡ كَسَبَتۡ فِیۤ إِیمَـٰنِهَا خَیۡرࣰاۗ قُلِ ٱنتَظِرُوۤا۟ إِنَّا مُنتَظِرُونَ
"....The Day that some of the Signs of your Lord do come, no good will it do to a person to believe then, if he believed not before, nor earned good through his Faith...." (6:158).
For someone who have already believed that there will be a literal end of the world, at the first glance, it seems this verse is saying, once the signs of the End comes, there is no beneft to believe anymore, because it it the end of the world, and it is just time for judgment, right?
Wrong!
Because according to the Imams, this verse is about Manifestation of the Qaim:
It is recorded in Bihar, that
Imam Ali and
Imam Sadiq said this verse denotes the advent of the awaited Qaim from us.
Now, let's think. How come, after Manifestation of the Qaim, there is no benefit for anyone to believe in Islam?
The answer is, because the Qaim comes with a new Revelation that supersedes Islam. He comes with a new Law from God, therefore the old Laws of Islam, is abrogated!
Consider, the Jews. When Jesus came, whoever believed in Jesus and followed His Injil, was considered a believer, and his deed was counted as good deeds in the sight of God. But once Muhammad came, believing and following Jesus, was not counted as a true belief, because at that time, belief in Muhammad was the touchstone of true belief.