First the cross is the deepest expression of God's love.
Second it is the best example of love towards our neighbor.
Third it is the greatest victory from the forces of evil.
And fourth the cross is the only atoning sacrifice for our sins.
I will quote some Scripture passages. I use the New International Version.
1. First of all the cross is powerful expression of the love of God towards us.
John writes in his first epistle, 1. John 4:9,10:
This is how God showed his love among us: He sent his one and only Son into the world that we might live through him. This is love: not that we loved God, but that he loved us and sent his Son as an atoning sacrifice for our sins.
In Christianity everything starts from God. He is the one who acts. It is written in Romans 5:8:
But God demonstrates his own love for us in this: While we were still sinners, Christ died for us.
2. Second the cross is a glorious example of unconditional love for us to follow.
The Holy Bible says in 1. John 3:16-18:
This is how we know what love is: Jesus Christ laid down his life for us. And we ought to lay down our lives for our brothers and sisters. If anyone has material possessions and sees a brother or sister in need but has no pity on them, how can the love of God be in that person? Dear children, let us not love with words or speech but with actions and in truth.
In the cross we see God's love in action. That should stir selfless love in us towards our neighbor.
3. Third the cross is the ultimate victory from the powers of evil.
Paul says in his letter to the Colossians, Col. 2:13-15:
When you were dead in your sins and in the uncircumcision of your flesh, God made you alive with Christ. He forgave us all our sins, having canceled the charge of our legal indebtedness, which stood against us and condemned us; he has taken it away, nailing it to the cross. And having disarmed the powers and authorities, he made a public spectacle of them, triumphing over them by the cross.
4. And last the cross is the most blessed vicarious sacrifice for our sins.
Vicarious means that there is someone who has died on our behalf. Jesus appeased God's holy anger by bearing the full penalty of our wickedness on the Calvary.
For all have sinned and fall short of the glory of God, and all are justified freely by his grace through the redemption that came by Christ Jesus. God presented Christ as a sacrifice of atonement, through the shedding of his blood—to be received by faith.
In Second Corinthians Paul writes, 2. Cor. 5:18-21
God -- reconciled us to himself through Christ and gave us the ministry of reconciliation: that God was reconciling the world to himself in Christ, not counting people’s sins against them. And he has committed to us the message of reconciliation. We are therefore Christ’s ambassadors, as though God were making his appeal through us. We implore you on Christ’s behalf: Be reconciled to God. God made him who had no sin to be sin for us, so that in him we might become the righteousness of God.
Dear brethren, be free. Your sins have been forgiven in the name of Jesus and through the power of his blood. Go in peace and serve the Lord and one another joyfully. Amen.