Peace I leave with you; my peace I give to you.
Not as the world gives do I give it to you.
Jesus is the only one able to promise peace and truly deliver it. Aside from him there are a wide variety of purported paths to peace in the world. And some of them may have some benefit, insofar as practicing virtue does help us be more free from the vicissitudes of the world than we would be otherwise. Others, however, advertise that we may find peace by destroying the parts of our humanity that long for joy and satisfaction. But this is not peace, but rather emptiness. And emptiness does not remain empty, but is quickly filled lesser and baser things. Only Jesus is able to give us something truly worthy of the name peace that is nevertheless not dependent on circumstances. It does not require us to ignore circumstances, nor always even to execute a perfect response to our circumstances. It is rather the gift from one who has conquered circumstances by conquering death itself. Jesus gives us his own way of thinking, rooted in trust of his Father, as a gift to renew our own minds. In no way does this gift depend on us except insofar as we must put it to use if it is to work in our lives.
Do not let your hearts be troubled or afraid.
Without care and prayer we can allow ourselves to slip into old ways of thinking which regard this world as ultimate and death as the final horizon of all striving. We are instead called to be transformed by the renewal of our minds (see Romans 12:2) so we can understand the genuine transcendent goods which are ours in Jesus, goods that neither time nor death can steal. Then we can set our minds on things above where Christ is seated at the right have of God and where our own life is, in some sense, already hidden with him (see Colossians 3:1-3). When our thoughts try to tell us that trouble and fear are the final world let us respond to them with the deeper truth that Christ has conquered death and he is victorious.
In the world you will have tribulation. But take heart; I have overcome the world (see John 16:33).
Part of the challenge for the disciples was going to be losing access to the visible presence of Jesus. He would be taken in death but return in the resurrection. He would be taken in his ascension but would come again in glory. Even after it became clear he was not defeated by death it nevertheless seemed surprising and difficult that the old familiar mode of his existence among them must end. Yet what he was doing by departing was something worth celebrating when properly understood. It was the glorification of his own humanity, and therefore in turn also that of all who were united to him. Hence all who loved him would truly rejoice that he went to the Father, for they were taken up together with him.
Wherefore He says, If ye loved Me, ye would rejoice, because I said, I go to the Father; for human nature should exult at being thus taken up by the Only Begotten Word, and made immortal in heaven; at earth being raised to heaven, and dust sitting incorruptible at the right hand of the Father.- Augustine
Jesus was on a mission to destroy the ruler of this present darkness, to disarm the principalities and powers (see Colossians 2:15), and to share the treasures they had previously horded with the world (see Luke 11:21-22, Ephesians 4:8). One sense of what the meaning of that treasure was that it contained precisely those fruits that we were meant to bear, the good works prepared in advance for us to do (See Ephesians 2:10). For these reasons and many others let us sing the victory of Christ.
Your friends make known, O Lord, the glorious splendor of your kingdom.