Q: When a person believes on Jesus Christ and His final payment for our sins on the cross and His rising from the dead, is that person saved from that moment?
A: Yes. Eternally saved and indwelt by the Holy Spirit until the day of bodily resurrection at the Rapture.
“In whom we have redemption through his blood, the forgiveness of sins, according to the riches of his grace; Wherein he hath abounded toward us in all wisdom and prudence; Having made known unto us the mystery of his will, according to his good pleasure which he hath purposed in himself: That in the dispensation of the fulness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth; even in him: In whom also we have obtained an inheritance, being predestinated according to the purpose of him who worketh all things after the counsel of his own will:That we should be to the praise of his glory, who first trusted in Christ.
In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise, Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.” (Ephesians 1:1-14 KJV)