St. Truth, you are learning at a young age that evangelical apologists give dangerously simplistic answers to bafflingly complex questions. At your age, I saw through these evasive tactics and almost lost my faith because of them, especially when I read that Jesus' erroneous prediction in Matthew 10:23 was a key reason why famed philosopher Bertrand Russell was an atheist. See his book, "Why I Am Not a Christian." What kept me from total renunciation of my faith was an electrifying spiritual experience that I recount in my thread "Speaking in Tongues and Spirit Baptism" in the "Spiritual Gifts" section of this site.
Here is my interpretation of 2 of the problematic sayings of Jesus in question:
(1) "Truly I say to you, there are some standing here who will not taste death until they see the Son of Man coming in His kingdom (Matthew 16:28)."
The scholarly consensus is that Mark is a source for both Matthew and Luke. So Matthew 16:28 edits Mark 9:1, which reads:
"Truly I say to you, there some standing here who will not taste death until the kingdom of God has come with power."
Matthew construes "kingdom of God has come with power" to mean "the Son of Man coming in His kingdom." But how did Mark interpret his phrase? Scholars answer this question by pointing to the unusual time reference "6 days later" in 9:2. Mark usually connects sections of his Gospel with the word "immediately." Why would Mark suddenly inform us of the exact length of time between Jesus' prediction and the Transfiguration? The standard scholarly answer is this: for Mark, it took just 6 days for the kingdom to come in power, when Moses and Elijah returned from God's kingdom to converse with Jesus on the Mount of Transfiguration.
If this is Mark's understanding, does it fully capture Jesus' original intent in Mark 9:1? Scholars doubt this because of the phrase "will not taste death until," which seems to point to an event further away than just 6 days. Perhaps, Jesus' understanding about the future was limited by His humanity and His consequent lack of omniscience, so that He wasn't clear about exactly what events His resurrection would usher in. If so, one might interpret Mark 9:1 to mean that in one sense the kingdom of God came in power through the Transfiguration; in another sense, its unique power manifested itself through the outpouring of the Holy Spirit on the Day of Pentecost (Acts 2).
(2) Matthew 10:23 rests in the midst of a Q section that preserves Jesus' missionary instructions to His disciples. Matthew is only interested in the 12, not in the 72 others who supported their mission. Q (from the German "quelle," meaning "source,)" is basically a collection of sayings of Jesus used by Matthew and Luke, but not by Mark or John, and is akin the Coptic Gospel of Thomas, which consists of 114 sayings of Jesus. Q seems to be the sayings collection that circulated west of the Jordan River, whereas the Gospel of Thomas is the sayings collection that circulated east of the Jordan.
We have already discussed how Matthew changes a reference to the coming kingdom into a reference to the coming Son of Man. Matthew seems to have made a similar insertion in 10:23, perhaps under the influence of his M source (Jesus material unique to Matthew). Consider, then, how 10:23 seems to be a reworded interpretation of Luke 10:1:
"Truly I tell you, you will not have gone though all the towns of Israel before the Son of Man comes (Matthew 10:23)."
"After this, the Lord appointed 70 others to go on ahead of Him into every town and place, where He Himself was about to come (Luke 10:1)."
In Luke 10:1, Jesus is commissioning an advance party of disciples to promote his message in preparation of a teaching tour by Jesus Himself. not in preparation for Jesus' Second Coming at His Parousia! We must consider the possibility that Matthew misunderstands his Q source to refer to Jesus' Second Coming. But it is also possible that Matthew means something like this: "When they persecute you in one town, flee to the next," because I want you to cover as much ground as possible to give people a heads up that I'm coming to visit them soon. so that a good audience can be gathered throughout Judea and Galilee.
St. Truth, This series of reflections illustrates a discipline called redaction criticism, i. e., a study of the editorial changes Gospels make in their sources and the reasons for those changes.