Of course, Jesus is not only the person giving the legacy of peace, he is also the Executor or Administrator of the legacy. When each of us makes a will, we know that we will not be alive to enact it. With Jesus it was different. He knew that he would rise from the dead in order to ensure that we received his legacy.
In addition, Jesus knew that he would send the Holy Spirit to bring his peace into the hearts of his people. Already in this passage, Jesus has mentioned several of the ways in which the Spirit will work in the lives of disciples. He would indwell them, he would instruct them. In addition, he would give them a sense of peace that would be similar to the peace that Jesus experienced.
Therefore, the peace that Jesus is promising is a unique type that is totally different from peace that the world gives. It is a peace that is heavenly, that comes from another world. At that time, the people of Israel were under the pax Romana, the Empire-wide system of peace that was imposed by the Roman Empire. It was a peace from another place, but it was not a peace that was linked to liberty or love for the subjects of the Empire.
The unique peace of Jesus is different in a second way, which is that it is internal and not merely external. External peace is often merely the absence of hostilities whereas biblical peace is the presence of serenity and calm.
A third difference found in the unique peace of Jesus is its certainty as opposed to the desire of well-meaning people to have peace. Many sincere people want their friends and family to have inner comfort and say so with their words of greeting. But they are unable to ensure it. Jesus guarantees his peace to his followers.
A fourth difference located in the unique peace of Jesus is its basis. The peace of the world is dependent often on circumstances (adverse events spoil it) or on possessions (what we accumulate) or on achievements (what we can do). Obviously there is nothing intrinsically wrong with wanting pleasant circumstances, nice possessions or good achievements. But it is folly to make them the basis of our peace.
The unique peace that Jesus offers is based on a relationship with himself by the Spirit through meditation on the Bible and in prayer. It is a peace that can and should be known no matter what happens in the world. Sadly, it is a peace that can be disrupted, but the main reason for this will be disobedience to Christ, which results in the Father’s disapproval of us.