Others have answered for a situation where an explanation is asked that was given earlier. I often give more or less repeated explanations without being asked.
I often have situations where I explain some effect and want to explicitly express different views on that point. Some people may think the explanations pretty redundant, others may think that rewording opens new perspectives.
In other words ... makes clear that a reformulation (with possibly a new insight) of the last statement follows.
That is, ... also signals that a new explanation of the already mentioned point comes.
Providing a bunch of alternative explanations is providing an important service to your audience. IMHO, if your mindset is on providing such a service, the risk of coming across as condescending is small.
Different people find different explanation approaches more or less intuitive, simple/complex or understandable. There's nothing wrong with this. It may be that everyone of us has their favourite explanation approach for a certain topic. IMHO it is important not to forget that there are often other approaches as well that are just as fine - and that other people may find a different one more intuitive.
I use Like I said, ... or As I mentioned earlier, ... to connect/provide cross references.
For example: We have two options to tackle this, O1 and O2. [Explanation of O1] As I said before, O2 is an alternative. This is what we need to do...
There is nothing condescending in giving people cross references.
What is IMHO condescending is stuff like using "it follows trivially" for "plan pencil + about 4 sheets of paper", or "just" as abbreviation for hours of exacting work for a beginner... You can "just" avoid that... ;-)