And as some spoke of the temple, how it was adorned with noble stones and offerings, he said, "As for these things which you see, the days will come when there shall not be left here one stone upon another that will not be thrown down." And they asked him, "Teacher, when will this be, and what will be the sign when this is about to take place?" And he said, "Take heed that you are not led astray; for many will come in my name, saying, 'I am he!' and, 'The time is at hand!' Do not go after them. Luke 21:5–8 (RSV)
It is said that Luther was asked what he would do if he knew Christ would return the next day. Luther promptly replied, 'I would plant a tree.'
Christians are to be about the work of the Kingdom here. We are confident of our Lord's promise that He will return, bringing with Him the new Heaven and new Earth. We know that since those things are in His hands, we need not be concerned about them. They will come in His time.
Until then, we continue fulfilling the Great Commission, going wherever the Gospel must be proclaimed, caring for the weak and oppressed, showing charity to the neighbor, and striving to heal the wounds inflicted by sin and death.
It is not that we ignore the Lord's return. It is not ours to control, nor should we attempt to force the Lord's hand. He will come. Therefore we have the freedom to live without fear, confident that planting a tree today is what we are to do.