Usage
In the Old Testament, the word salvation is recorded 119 times in the King James Bible. It is derived primarily from three Hebrew words. The first of these, yeshuah (Strong's Concordance #H3444), can mean receiving salvation physically (Exodus 14:13) or spiritually (Isaiah 52:7). Yesha (#H3468) can reference being rescued or made safe (1Chronicles 16:35). Teshuah (#H8668) means rescued or delivered in a physical or spiritual sense.
In the New Testament, the word salvation is found 45 times and is derived from two Greek words. The first, soteria (Strong's #G4991), is by far used the most.
So then, my beloved, even as you have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation (soteria) with fear and trembling (Philippians 2:12).
The second Greek word, soterion (Strong's #G4992), the neuter version of soteria, is used in five places.
Therefore, take up the whole armor of God so that you may be able to resist in the evil day, and having worked out all things, to stand . . . And put on the helmet of salvation (soterion), and the sword of the Spirit, which is the Word of God (Ephesians 6:13, 17).
Overview
The Godhead (the Father and Jesus Christ), before anything existed, decided to pursue the greatest goal that would ever exist. Motivated by perfect love, they desired to share the same perfect and eternal existence they possessed with others. These beings, however, would first have to develop the kind of holy righteous character that would qualify them to receive such a gift.
The first beings given the power to develop character were the angels. Lucifer's rebellion, however, along with how quickly his lies were believed, called for another type of being to be created. God decided to create humans, made of flesh, and give them a chance to qualify for a perfect and eternal existence. His plan to bring as many humans as possibly into his family is called salvation.
Three Part Plan
One major aspect of God's salvation plan is the three-part timetable he decided to use to offer, personally, each human a chance to repent and build righteous character.
The first phase runs from Adam's creation to the Second Coming of Christ. During this period only a relatively few individuals will be called and converted. These people, however, will receive a rigorous training in righteousness. Their character will be built and shaped by having to overcome not only their own human nature, but also by resisting the constant onslaught of temptation from both Satan and the world.
Second Phase
The second phrase begins with Jesus' Second Coming. His Millennial reign, aided by those in the first resurrection, will bring God's Kingdom to earth. Satan's evil influence will not be allowed for 1,000 years (Revelation 20:1 - 2). Those offered salvation would build righteous character through overcoming their human nature as well as the negative influences of others.
Last Phase
The third and perhaps greatest phase of the salvation timetable takes place after the Millennium. All those who lived from Adam to Jesus' return, the unwashed masses whose minds were never fully open to comprehend the truth, will be resurrected and given a new physical body.
God will then open each person's heart to finally understand the truth, repent, and receive his spirit. After they live a life of overcoming (possibly for up to 100 years, Isaiah 65:17 - 20), those who are faithful to the end will be given God's salvation gift of eternal life. They will then join the rest of humanity in peace and harmony forever.