Your Question: There are so many things contrary to Jesus’ teaching in the Bible, e.g. the deception of Jacob, killing enemies. How is that possible? Does the end justify the means?
For several reasons there are many things in the Bible that are hard to square with Jesus’ teaching.
Not everything is an example to follow
First, not everything in the Bible is an example to follow. There are many stories that are warnings to us rather than examples. Jacob deceiving others is an example of that. A story in itself does not tell us whether what happens in the story is good or bad. We need the rest of the Word of God to determine whether it is good, bad, or a mixture of both. Much of what is in the Bible that is contrary to the teaching of Jesus, is there because the Bible is a book about people, and people are sinners.
Situation
Second, we need to know whether a word of Jesus applies to a situation or not. Jesus told us to love our enemies (Matthew 5:44). But He also told us that at the end of times God will send his enemies into eternal punishment (Matthew 25:46). So God’s command to love is not contrary to God’s punishment of evildoers. You can even say that because God loves people, evil cannot remain unpunished.
Difference between Old and New Testament
Third, there is a difference between how God deals with his people in the Old Testament and how He deals with them in the New Testament. In the Old Testament, the Lord promised many earthly blessings and meted out earthly punishments. This included commands to Israel to fulfill God’s judgment on peoples that had sinned consistently and terribly against Him.
In the New Testament, God promises heavenly blessings to his people. There is a much stronger focus on eternal life. God’s judgment is still an important of the message, but that judgment will come on the Last Day. Jesus himself will be the judge. We as believers in this age do not have to judge. We just have to love people and proclaim the Gospel, so that sinners will repent and turn to God.
Higher plane
Fourth, in the teaching of Jesus, the glory and the loveliness of God is displayed in a way that could not be found in the Old Testament yet. The Bible says that in Christ “all the treasures of wisdom and knowledge” are hidden (Colossians 2:3). “In him the whole fullness of deity dwells bodily, and you have been filled in him” (Colossians 2:9,10). No wonder then that since Christ came to express who God really is, God’s children are called to live on a higher plane, displaying more love than we see in the Old Testament. But this should not be taken so far as to suggest they are opposites. In the Old Testament as well as in the New Testament we encounter God as both loving and righteous.