When we face the loss of a loved one it is natural for us to grieve. Jesus Christ said to His followers in His Sermon on the Mount, "Blessed are they that mourn: for they shall be comforted." When we encounter a person with grief we can only have compassion for their sorrow. This is how we express our love and understanding. It is not necessary to say much: "I am sorry," a hug, a feeling of empathy for the sorrow they experience.
For Christians this sorrow should not last long. We can remind ourlselves of the Passion of Christ and how He accepted the Cross for our benefit. In His death we learned of the Resurrection and the promise of eternal life.
Elder Macarius says,
In the ground of the Christian heart, sorrow for the dead soon melts, illumined by the light of true wisdom. Then, in place of the vanished grief, there shoots up a new knowledge made of hope and faith. This knowledge does not only wash the soul of all sadness; it makes glad.
Ponder these words:
Though our outward man perish, yet the inward man is renewed; and: If our earthly house of this tabernacle were dissolved, we have a building of God, a house not made with hands, eternal in the heavens (II COr 4:6, 5:1).
Reference: Russian Letters of Spiritual Direction, p 41, 45