Christians have different views on how Christians should respond to the OT, in light of the Gospels, Epistles, etc.
i take the OT as an historical, literal description of the events surrounding the creation of the world, the fall and dispersal of man, the forming of various nations, the calling of Abram, the calling of the Hebrews from Egypt, the founding of the Hebrew nation in present-day Israel, and the nation's history.
it is true that God commands a lot of bloodshed in the OT. in the greater historical context of the Bible, this is action taken against specific peoples, nations, and cities in response to their sin, arrogance, violence, and evil. so God in effect uses other nations (including the Hebrews) to punish, subdue, wipe out, or humble these peoples. and Israel also gets kicked a number of times by the Babylonians, Assyrians, ect. each of these nations being used by God to humble and correct His people.
so in effect, God uses nations to subdue and punish nations.
so why does God disallow killing in the Gospels if He was all for it previously?
the previous acts of violence were carried out in response to sin, evil, arrogance, and injustice.
Christians believe that Jesus is the Messiah, the promised one through whom peace will come, and rule. so under Jesus' rule, in the life of the Christian, one is to love one's enemies, turn the other cheek, forgive wrongs, and serve all. God still punishes sin and error in the NT, sometimes with suffering and death (Luke 19:41-44 and Acts 5:1-9). but the Christian is to understand that it is God's job to punish evil, not ours.
many also argue that Christians ought to follow Mosaic Law, including keeping Saturday as a day of rest, and refraining from pork. yet Mosaic Law, while important, was given to the Hebrews, not the world. Jesus came for His own people, and also for all nations. we believe the Mosaic promise was fulfilled in and through Jesus, who technically broke Mosaic Law by healing and allowing people to do work on the Sabbath. hence many Christians would argue that Mosaic Law does not bind the believer in Messiah, as in Him we are justified with God not by what we do, but by faith in God's Son, and His grace.
some Christians do worship on Saturday, refrain from pork, etc. and i don't see a problem with that at all. but ultimately it's Jesus, and not Mosaic Law, which is central for us. Jesus rephrased the commandments of God for all people, into two- (
Mark 12:28-31). He also healed on the sabbath, declared that it is what we say and express rather than what we eat which makes us unclean, and ate with sinners and tax collectors. we believe that as Messiah He is greater than Moses, came for all peoples, and that He fulfills a promise made with humanity stretching back before Moses- to Abraham and even to Eve.
so in other words, i would argue that it is not necessary for a believer in Jesus to adhere to Mosaic Law, but to the Law given in and through Jesus the Messiah, the one Moses wrote about, who came for all nations, to show and give the grace of God.