The Hebrew word for saint is “qodesh” and the Greek word for saint is “hagios”. Both are translated not only “saint” but “holy” in the English versions of the Bible. The short definition is “set apart” or “sanctified”.
When God created humanity He created them as a special class of animals. All animals are called living souls, but only the human animal will be made into His image…
“And the LORD God formed a human out of the dust of the ground, and breathed into his nostrils the breath of life; and the human became a LIVING SOUL…in the image of God He created him; male and female He created them…” (Genesis 2:7, 26-27)
Humanity was holy (set apart/sanctified) to become the image of God. All humans will be born again after death into the "image of God". Believers in this life at the return of Jesus to set up the millennial reign on this Earth, and all the rest of humanity will be made alive into the image of God after death is abolished following the events of the Great White Throne.
"But the fact is, Christ has been raised from the dead, the first fruits of those who are asleep. For since by a man death came, by a man also came the resurrection of the dead. For as in Adam all die, so also in Christ all will be made alive. But each in his own order: Christ the first fruits, after that those who are Christ’s at His coming, then comes the end, when He hands over the kingdom to our God and Father, when He has abolished all rule and all authority and power. For He must reign until He has put all His enemies under His feet. The last enemy that will be abolished is death." (1 Corinthians 15:22-26)
“...the end of your faith is the salvation of your souls...concerning this salvation, the prophets seek out and search out, who prophesied of the GRACE which is for you...testifying beforehand to the sufferings pertaining to Christ and the glories to follow...expect perfectly the GRACE to be brought to you at the appearance Jesus Christ...as He Who called you is Holy, you also became holy...” (1 Peter 1:9-16)
“For the wages of sin is death but the free GIFT of God is eternal life through Jesus Christ our Lord…It is by GRACE you have been saved through faith, and this not of yourselves, it is a GIFT of God, not of works…for the saving GRACE of God has made its advent to all humanity...anticipating that happy expectation, even the advent of the glory of the great God and our Savior, Jesus Christ, Who gives Himself for us, that he should be redeeming us...". (Romans 6:23; Ephesians 2:8-10; Titus 2:11, 13-14)
Humans are saints (holy) because God set us apart to be made into His image. Even though all saints become sinners in this mortal life, some worse than others, God will save us all and change us into a new creation - holy and His image!