So the one and only way that there has ever been to become saved is by grace through faith, and by the same grace through the same faith we are therefore required to be careful to obey all of God's commands. As such, there is no reason to consider
Luke 16:27-31 to be speaking about obedience apart from faith. A relationship with Christ is the goal of the Law for righteousness for everyone who has faith (
Romans 10:4), ...
.
The OT Jews kept the Law because they had faith in God and His Law, eg Moses, Elijah, King David, beggar Lazarus, etc. These law-abiding and faithful Jews were eventually saved from hell after death.
Jews like Moses, Elijah and beggar Lazarus who lived before the 1st Advent of Jesus Christ and the Cross on earth in
000BC, did not have the opportunity to place their faith on Jesus as their Christ/Messiah while they were still living on earth, but only to place their faith on Moses Law.(LUKE.16:19-31)
... Only after death, did they had the opportunity to place their faith on God's Son and be saved from hell.(1PETER.3:19, MATTHEW.17:3)
... In comparison, the rich Jew who refused to give charity to Lazarus ended up in hell after death for unrepentantly breaking God's Law/commandment at DEUT.15:11 and was not given the opportunity to hear Christ's gospel after death.
There is a big difference between having faith in God's Law(= before and after 000BC) and having faith in God's Son(= only after 000BC), even though both require faith, ie the reward or blessing from God is different. The former brings reward for this life on earth(DEUT.28, ROMANS.2:10) while the latter brings reward for the afterlife after death or leaving this rotten earth.(JOHN.3:16)
... IOW, most people who live after 000BC already have the opportunity to place their faith in God's Son - Jesus Christ, eg today.
The Jews today still have faith in God and His Law or Moses Law = the Jews have been blessed by God with a good and long life on earth. But because they refuse to have faith in God's Son - Jesus the Christ/Messiah, they miss the additional reward of eternal life after death. Today, they are still waiting for their Messiah/Christ.
... Similarly for the Muslims.
HEBREWS.11: = 6 But without faith
it is impossible to please
Him, for he who comes to God must believe that He is, and
that He is a rewarder of those who diligently seek Him.