Some would argue, that from the exterior at least, the Divine Mercy Chaplet would appear to be just a little more customized towards prayers for the holy souls in Purgatory ; in particular the clause “Have Mercy on us and on the whole world”. Similarly, it is also a very powerful prayer for the dying - when said with trust in the Divine Mercy. But the thing about the Divine Mercy Chaplet is that even if we are offering it for the souls in Purgatory, we must still recite a Hail Mary after the initial Our Father opens the Chaplet.
In a comparison of the two - the
Rosary and the
Divine Mercy Chaplet, from the perspective of their applicability to helping the holy souls in Purgatory , Father Robert Stackpole, STD,- Director of the
John Paul II Institute of Divine Mercy concludes in his article
Is the Chaplet Only for the Living and Dying ?-
Either prayer, offered up with a sincere heart that trusts in the Lord, will not fail to be heard, and opens the floodgates of Divine Mercy.
Also, from Fr. Dan Cambra of the Marians of the Immaculate Conception, a good article on our Blessed Mother and Purgatory :
She Knows them Well. How can She Assist the Souls in Purgatory
The Holy Sacrifice of the Mass is the most powerful prayer which can be offered for the holy souls in Purgatory. But after the Mass, the next most powerful prayer which can be offered for the holy souls, according to prevalent thought of today and of time past, is the Rosary. It is not only prayed
to our Blessed Mother - it is prayed* with *Her.
A nice, related,comprehensive
National Catholic Register article in the form a Q&A interview with author Susan Tassone entitled :
How to Help the Holy Souls in Purgatory