If You're Not Catholic
Does Jesus reject someone who is not sacramentally baptized?
Although our Lord did not reveal to St. Faustina the extent to which the extraordinary graces of Divine Mercy Sunday are available to non-Catholics, it is theologically certain that anyone who is seeking Jesus with a sincere heart and trusts in His love and mercy will be richly blessed on that day: "No one who comes to Me shall ever be hungry, no one who believes in Me shall ever thirst. No one who comes will I ever reject" (Jn. 6:35-37).
Just as in the Baptism of desire the first grace that forgives original sin is present in the original longing or turning to God, even of a person not sacramentally baptized, a mere desire to receive the Eucharist already bestows grace which gives spiritual life. (Cf. St. Thomas Aquinas, Summa Theologiae, 3a. 79,1.)
Non-Catholics, therefore, may participate in the celebration of Divine Mercy Sunday by making a Spiritual Communion with great trust, since it is by the degree of trust that we receive graces.
Act of Spiritual Communion
My Jesus, I believe that You are present in the Blessed Sacrament.
I love You above all things and I desire You in my soul.
Since I cannot now receive You sacramentally,
come at least spiritually into my heart.
As though You were already there,
I embrace You and unite myself to You;
permit not that I should ever be separated from You.