The OT saints had to wait in Abraham's bosom until Christ provided the means of reconciliation by the blood of the Lamb. They had been chosen for salvation through their faith in God, but they had NOT been washed with His blood, which fully justified them, and allowed them to enter the kingdom of God, as stated in Hebrews 12:22-23.
Think of it this way: Not justified by the blood of the Lamb = Not made Perfect.
Justified by the blood of the Lamb, by the washing of regeneration = Made Perfect.
Now you might ask just how does the above relate to Hebrews 5:7-9? Christ was "Made Perfect" with His suffering and death, meaning He was made complete, the perfect sacrifice for sin. He had prayed that if possible, let this "cup" pass from Him, but He was committed to doing His Father's will. The suffering and death was necessary for Christ to be made perfect. Later that evening, Christ expressed His full commitment to His suffering and death, see John 18:11.
One last point, in Hebrews 5:8 Jesus is said to have "learned obedience" from His suffering. That in my opinion completely misses the meaning. Christ perceived the need to submit His Father's will, which necessitated His suffering and death. No greater Love...
Hebrews 5:8 (Interpretive Translation)
Although He existed as the incarnate Son, He perceived Himself to be obedient by His intended suffering and death.
Think of it this way: Not justified by the blood of the Lamb = Not made Perfect.
Justified by the blood of the Lamb, by the washing of regeneration = Made Perfect.
Now you might ask just how does the above relate to Hebrews 5:7-9? Christ was "Made Perfect" with His suffering and death, meaning He was made complete, the perfect sacrifice for sin. He had prayed that if possible, let this "cup" pass from Him, but He was committed to doing His Father's will. The suffering and death was necessary for Christ to be made perfect. Later that evening, Christ expressed His full commitment to His suffering and death, see John 18:11.
One last point, in Hebrews 5:8 Jesus is said to have "learned obedience" from His suffering. That in my opinion completely misses the meaning. Christ perceived the need to submit His Father's will, which necessitated His suffering and death. No greater Love...
Hebrews 5:8 (Interpretive Translation)
Although He existed as the incarnate Son, He perceived Himself to be obedient by His intended suffering and death.