They lived under the various OT laws and will be judged by that OT law they lived under. Salvation under the OT had different requirements than the NT gospel of Christ that we today who live under. The NT gospel of Christ requires belief repentance cofession and baptism for remission of sins (Jn 3:16; Lk 13:3; Mt 10:32-33; Mk 16:16) which was not available to them under the OT law.
You mean like..."Dispensationalism?"
The saints of the Old Covenant will be judged BY the Old Covenant?
Deu_33:2 And he said, The LORD came from Sinai, and rose up from Seir unto them; he shined forth from mount Paran, and he came with ten thousands of saints: from his right hand went a fiery law for them.
Deu_33:3 Yea, he loved the people; all his saints are in thy hand: and they sat down at thy feet; every one shall receive of thy words.
1Sa_2:9 He will keep the feet of his saints, and the wicked shall be silent in darkness; for by strength shall no man prevail.
2Ch_6:41 Now therefore arise, O LORD God, into thy resting place, thou, and the ark of thy strength: let thy priests, O LORD God, be clothed with salvation, and let thy saints rejoice in goodness.
Job_5:1 Call now, if there be any that will answer thee; and to which of the saints wilt thou turn?
Job_15:15 Behold, he putteth no trust in his saints; yea, the heavens are not clean in his sight.
Psa_16:3 But to the saints that are in the earth, and to the excellent, in whom is all my delight.
Psa_30:4 Sing unto the LORD, O ye saints of his, and give thanks at the remembrance of his holiness.
Psa_31:23 O love the LORD, all ye his saints: for the LORD preserveth the faithful, and plentifully rewardeth the proud doer.
Psa_34:9 O fear the LORD, ye his saints: for there is no want to them that fear him.
Psa_37:28 For the LORD loveth judgment, and forsaketh not his saints; they are preserved for ever: but the seed of the wicked shall be cut off.
Saints...in the Old Covenant...so, what is a saint?