Adapt yourself to the things among which your lot has been cast and love sincerely the fellow creatures with whom destiny has ordained that you shall live.

This quote is asking you to accept the circumstances you have been given in life and to show genuine love to the people you know and who are around you. It means that if you do not like the situation you are in, you should still try to make the best of it. You should not be hostile or negative to the people in your life, but try to have empathy, understanding, and compassion towards them.