Setting aside his divinity, Jesus came to the earth in human form. He went from greatness to being the least. He did this because he loves us and wants mankind to have a life with him and his father.
2 Corinthians 8:9 New American Standard Bible
9 For you know the grace of our Lord Jesus Christ, that though He was rich, yet for your sake He became poor, so that you through His poverty might become rich.
Philippians 2:5-8 Easy-to-Read Version
5 In your life together, think the way Christ Jesus thought. 6 He was like God in every way, but he did not think that his being equal with God was something to use for his own benefit. 7 Instead, he gave up everything, even his place with God. He accepted the role of a servant, appearing in human form. During his life as a man, 8 he humbled himself by being fully obedient to God, even when that caused his death—death on a cross.
John 10:9-11 Complete Jewish Bible
9 I am the gate; if someone enters through me, he will be safe and will go in and out and find pasture. 10 The thief comes only in order to steal, kill and destroy; I have come so that they may have life, life in its fullest measure. 11 “I am the good shepherd. The good shepherd lays down his life for the sheep.
God had his plan of salvation already worked out before he created mankind. Before anything was created, God planned to allow humans who willingly followed him, his immortal children.
Ephesians 1:4-5 English Standard Version
4 even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. In love 5 he predestined us for adoption to himself as sons through Jesus Christ, according to the purpose of his will,
2 Timothy 1:9 International Standard Version
9 He saved us and called us with a holy calling, not according to our own accomplishments, but according to his own purpose and the grace that was given to us in the Messiah Jesus before time began.
When accepting Jesus as our saviour is the only way to be saved, how could those who died before the sacrifice of Jesus, be saved from their sins?