The relationship of a child with its mother is a unique relationship.
For God so loved the world, that He gave his only Son, that whoever believes in Him should not perish but have eternal life.
John 3:16(ESV)
The relationship of a child with his or her mother is a unique relationship. From the moment the child is conceived to the point where they are completely self-sufficient, a mother cares and protects her child. The mother knows that when she becomes pregnant, she will have to make sacrifices for the child or else that child will die. She loves her child and makes sacrifices within her own life to ensure the child is nurtured, protected, and healthy.
The relationship of God with His people is similar to this unique relationship. God knows His people. According to Psalm 139: He knows them before they are born.
When someone is born again, as the rest of John 3 speaks to, they enter into a new and unique relationship. A relationship made possible through the work of Jesus Christ.
As a child’s life is reliant upon its mother, so our spiritual life is reliant upon Christ and His work on the cross. God sent Jesus to die on the cross out of love for His people. Because of that sacrifice, those who place their faith in Christ are no longer condemned to a life separated from God forever. Instead, those who place their faith in Christ are given the gift of eternal life with Him. Those who have placed their faith in Christ are now born again and sustained by God through the Holy Spirit just as a mother sustains a child.
We rely on God for spiritual life, food, and safety. Because of His love, we are saved. Because of His sacrifice, we are saved.