Washington is expressing his view that all good things that come to men should be earned by their efforts. By 'struggle' he means through constant work and development that will be faced in trying to make the future easier for those who will come after us. If things are easier for others as a result of our work, then those privileges are rewarding, but if those privileges are given to some through 'artificial forcing' or a system of made up comforts for royals or heads of state who claim to own them as a divine gift, then there is no progress or enjoyment, only privileges reserved for the few.