Per your question, “Then turn around and basically say that YOU know the mind of God (because He is calling us back, period of Divine Mercy, Divine Justice, etc). And you know this how? ”
Read St. Faustina’s Diary (the revelations to Faustina are approved by the Church) where Jesus tells her innumerable times about this present period of His Mercy which will be followed by His Divine Justice. Others describe this more completely, as here:

(summary of a retreat talk by Willy Effinger)

My dear friends, over the past fifteen years, I have given many talks and workshops on different aspects of God’s Divine Mercy, but none is more unsettling than the topic of the last days! Even though each of us will have to face the Day of Justice, we must focus on the present; we must realize that we are living in the Time of Mercy.

There are many entries in St. Faustina’s Diary dealing with this subject, so I have picked 15 of them to demonstrate the urgency of preparing ourselves for what many refer to as the “end times”. As Christians, it is not good for us to live in fear; rather, we should place hope in what is revealed in the Word of God. So, let us dive into the warnings; let us read some of the entries from “Divine Mercy in My Soul”. (St. Faustina’s Diary)

In 1934, at the outset of St. Faustina’s writings, the Lord said to her:

“Write this: before I come as a Just Judge, I am coming first as the King of Mercy. Before the day of justice arrives, there will be given to people a sign in the heavens of this sort: All light in the heavens will be extinguished, and there will be great darkness over the whole earth. Then the sign of the cross will be seen in the sky and from the openings where the Hands and the Feet of the Saviour were nailed will come forth great lights which will light up the earth for a period of time. This will take place shortly before the last day.” (entry #83)

In entry #570, St. Faustina recorded an encounter with the Lord where He spoke these words to her: “… Your assignment and duty here on earth is to beg for mercy for the whole world. No soul will be justified until it turns with confidence to My mercy and this is why the First Sunday after Easter is to be the Feast of Mercy.

On that day, priests are to tell everyone about My great and unfathomable mercy. I am making you the administrator of My mercy. Tell the confessor that the Image is to be on view in the Church and not within the enclosure of the convent. By means of this Image, I shall be granting many graces to souls; so let every soul have access to it.”

Although the Lord spoke these words to a Polish nun behind convent walls, He is also speaking today to all those who sincerely have taken up the call to Divine Mercy, all the souls who promote His message of Divine Mercy, all those who try to be “as merciful as the Heavenly Father is merciful”. It is our acts of mercy that will bless our neighbourhoods; living mercy is what will change the world! Keep in your heart the words that Jesus spoke: “no soul will be justified until it turns with confidence to My mercy.”

On March 25th in 1936, the Mother of God weighed in on this topic as well. While St. Faustina was in deep meditation about the immeasurable greatness of God and on His condescension to His creatures, Mary appeared to her and said: “O how pleasing to me is the soul that follows faithfully the inspirations of His grace! I gave the Saviour to the world; as for you, you have to speak to the world about His great mercy and prepare the world for the Second Coming of Him who will come, not as a merciful Saviour but as a Just Judge! … Speak to souls about this great mercy while it is still the time for mercy. If you keep silent now, you will be answering for a great number of souls on that terrible day. ”
Also: http://catholicharboroffaithandmorals.com/Mercy%20and%20Justice.html