Kedoshim 

קדושים

One cannot be satisfied with the world as he received it from those who preceded him; he must seek to improve it so those who succeed him will enjoy it as he did. 

“When you shall come into the land and plant” (Leviticus 19:23): The Holy One, blessed be He, said to the Israelites: Even though you will find the Land of Israel filled with everything good, do not say: We will sit idly and will not plant. Rather, be vigilant in your planting, as it is stated: “And plant any food tree” (19:23). Just as you entered and found trees planted by others, so too, you shall plant trees for the benefit of your children. In order that a person will not say: I am old and tomorrow I will die; why should I exert myself for others? Solomon said: “He made everything beautiful in its time; He put the world [<source>(<i>Tanĥuma</i>, <i>Kedoshim</i>) </source>