Alright .... so ... in laymen's terms, here is what I believe, myself.
God made heaven and earth ... and He made man and woman in His likeness. He put man and woman in the garden He made, called Eden. In that garden, besides trees to sustain the body, God put two other trees. The tree of the knowledge of good and evil, and the tree of life.
God said not to eat from the tree of the knowledge of good and evil for we would die in that day, if we did ... and yet ... we did. From that moment forth (and for 4000 years hence) we were denied the tree of life, cast out of the garden, and now in a state where God could not walk with us as He did, for God is Holy, and anything less than holy cannot come into God's presence without being destroyed. For 4000 years we paid the wages sin pays ... death.
All the while, though, God, who is merciful, is consoling us with the knowledge that He has a plan to remedy our state of separation from Him. Speaking through many of His chosen prophets He points to a day of salvation ... or reconciliation to Himself.
That salvation came in the form of Jesus Christ, the Messiah, Son of God. Born of the Holy Spirit, he was not under the curse we have all been born into. He lived a sinless life. He became the perfect "lamb" of sacrifice for sin-filled man. He was crucified bearing all of mankinds sins (6000 years worth of sins). He died, went down and collected the keys of death and hades, was raised again to life and now sits at the right hand of the Father.
"For God so loved the world that He gave His only-begotten son, so that whoever should believe in him would have eternal life." John 3:16
We are saved by belief in God's plan for reconciliation: Jesus Christ, Messiah.
When we believe, God seals us with His Holy Spirit and we are adopted as sons and daughters. We are given a new spirit and a new heart and are sanctified as holy in these. God (Father, Son and Holy Spirit) dwells with us and we with Him in these holy inward parts.
And as we walk with the Lord in these inward parts, our outward parts are sanctified as well, and we bear His fruits.
We know we are saved because God is true and cannot lie, and His Spirit testifies with our spirit that we are His ... and we exclaim Abba, Father!
Noone and nothing can snatch us out of His hand for there is no one and nothing greater than He... nor can we jump from it willingly ourselves, for neither are we greater than God. If we have been sealed by the Holy Spirit we can be confident in His promise to us of everlasting life with Him.