The early Christians, in praying for their dead were expressing
their belief that departed brothers and sisters underwent a
purification after death ("purgatory").
 
Their prayers were prayers that God would have mercy on them
during this time of healing and purification.
Many people who do not share the Catholic Christian faith
life have difficulty with the appearance that in their prayers,
Catholics appear to pray to the Saints, to Mary, as one prays
to God. This "praying to" appears to them to indicate a worship
of the Saint as if giving to the Saint or Mary what is due to
God alone.