There are several meanings of Cross
1. Cross means PLUS (+). Plus means union – Union with God
2. Plus means to add – add the divine qualities
3. Vertical line represents EGO and EGO is cut by a horizontal line. Cutting the vertical line means cutting the EGO. So without Ego there is no duality, without ego we are one with God.
4. It recalls us the life, teachings and qualities of Jesus Christ. Jesus was the embodiment of compassion, forgiveness and love.
5. Cross indicates to be free from the fear of death. Jesus said, “Carry your own cross” and “carry your cross and follow me”. He meant to be free from the fear of death and to follow him to achieve the eternal life of divinity.
Source: Pages 10-12, Chapter 3, Mysticism of Religious symbols by Paramhansa Hariharananda.