As was said in another reply, we offer with Jesus, the Body, Blood, Soul, and Divinity and suffering of Jesus to the Father at every Mass as we are made present at the Crucifixion of Our Lord. The Mass is the re-presentation of the Sacrifice on Calvary. To God all points of time and space are eternally present in their immediacy (CCC 600) and it is Catholic Faith that God makes present the one Sacrifice of Christ for all at the Mass and we are there with Mary as She “resolutely unites her prayer with the prayer of Jesus” (CCC 2741, 2740, 2666, 2668), in His name, for all sinners, and He prays His prayer with her and in her and through her, uniting His prayer to her, as He will do for each of us if we ask Him to make His prayer our prayer with no additions or deletions on our part because we believe His prayer is the perfect prayer for each and every person at every point of space and time.
Since we are all sinners, both by commission and omission, our prayers and voluntary sacrifices are of no real value, (we, by our own efforts can do nothing to help ourselves unless we unite ourselves to Christ in the Faith that He is true God and True Man) whereas the sacrifice of Christ was of infinite value and the only best way God could redeem and reconcile all sinners after sin entered creation.
So when we pray the Chaplet of Divine Mercy and we offer God “the Body, Blood, Soul, and Divinity” of Jesus Christ we are implicitly joining with the Prayer of Jesus and asking Him to pray His prayer in us, for us, and through us as we resolutely unite our prayer with His prayer and by extension, unite our prayer with His prayer through, with, and for His Mother Mary at the foot of the Cross as she prays for all sinners, for all her children. I hope this helps.
