Lucilius' position in life and what he does for his business is unknown. But it sounds like he is quite deep in many ventures and he may hold a position of prominence. At the same time, it seems that Lucilius is trying to embrace a life of complete philosophy and he is allowing his business is keeping him from jumping in with both feet.
I couldn't help but put myself into this letter and pretend that Seneca were writing to me. It made me wonder if I am like Lucilius and am making up excuses as to why I can't or won't embrace a life of complete philosophy.
The first part of the letter is centered around the them of being present in the moment or mindfulness. The Stoic concept is called prosoche. And in this case, with Lucilius, Seneca is counseling him to look for opportunities to escape the life of business:
you must withdraw yourself from those showy and depraved pursuits ... You must be not only present in the body, but watchful in mind, if you would avail yourself of the fleeting opportunity. Accordingly, look about you for the opportunity; if you see it, grasp it, and with all your energy and with all your strength devote yourself to this task, – to rid yourself of those business duties.
Watching and waiting for the opportune time to depart that (business) life and then to act when that opportunity presents itself - that is what Seneca suggests. Seneca makes the point that it can be done little by little.
But I likewise maintain that you should take a gentle path, that you may loosen rather than cut the knot which you have bungled so badly in tying, – provided that if there shall be no other way of loosening it, you may actually cut it. ...
hasten as fast as he can, and beat a retreat before some stronger influence comes between and takes from him the liberty to withdraw. But he also adds that one should attempt nothing except at the time when it can be attempted suitably and seasonably. Then, when the long-sought occasion comes, let him be up and doing.
Seneca observes some common worries of business and what a good man would think of them.
a good man will not waste himself upon mean and discreditable work or be busy merely for the sake of being busy. Neither will he, as you imagine, become so involved in ambitious schemes that he will have continually to endure their ebb and flow. ... From business, however, my dear Lucilius, it is easy to escape, if only you will despise the rewards of business. We are held back and kept from escaping by thoughts like these: "What then? Shall I leave behind me these great prospects? Shall I depart at the very time of harvest?" ... Hence men leave such advantages as these with reluctance; they love the reward of their hardships, but curse the hardships themselves.
And then this spot-on quote: "there are a few men whom slavery holds fast, but there are many more who hold fast to slavery."
Become free. Shed stuff. You won't and can't take anything with you. Life is a pursuit of virtue and wisdom and by discarding all the indifferents, you become free to focus on the most important. The urgency should be the same as if you were thrown overboard a ship with all your possessions. Get to the shore! Leave the junk behind.
if you keep turning round and looking about, in order to see how much you may carry away with you, and how much money you may keep to equip yourself for the life of leisure, you will never find a way out. No man can swim ashore and take his baggage with him. Rise to a higher life.
Focus on and love virtue and wisdom. Stop starting and start finishing the objective.
No one has anything finished, because we have kept putting off into the future all our undertakings. ...
You've learned what life offered to teach you if you are at peace every day up to the day you die. If you can live and die well, then philosophy reached you. But if the thought of death causes intense anxiety, then you have philosophical work to do. Philosophy is nothing more than preparation for death.
A man has caught the message of wisdom, if he can die as free from care as he was at birth; but as it is, we are all a-flutter at the approach of the dreaded end. Our courage fails us, our cheeks blanch; our tears fall, though they are unavailing. But what is baser than to fret at the very threshold of peace? ...
Men do not care how nobly they live, but only how long, although it is within the reach of every man to live nobly, but within no man's power to live long.