It absolutely is NOT important at all to know all of the companies in a given index. The Dow has just 30 companies, so while it's not important to know them, it is likely that most attentive investors will know most of them off the top of their head (I know most of them, but I wouldn't be able to name all 30).
Investing is not nearly as complicated as many like to believe it is. Too many attach bravado and intelligence to it when that's a bogus way to look at it. NO ONE can time the market. NO ONE can accurately predict what will happen to the market on a regular basis. Any calls that seem right on are just chance happenings and can not be repeated. The absolute best way to invest is to just do it...consistently and repeatedly. The market has proven to go up over time. You invest money you don't need today so that you have money later on when you no longer have an income. That's it. It's not sexy. It's not rocket science. It requires next to no knowledge about indices. If the market as a whole drops a ton and you have extra money to invest, it's not a bad idea to throw it in at that time (because the market WILL go north again), but that should always be EXTRA investing. You should have a set amount (at least 15% of your income) that goes into retirement accounts at all times regardless of market conditions. You should NEVER not be investing and waiting for a big drop before you purchase.