Looking at the lower and upper trigrams:
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The Fourth line marks the begining of the upper trigram. While
the lower trigram is internal – focused on and absorbed in its own
process, the upper trigram steps out into the world of the other. Lines
1, 2 and 3 (starting at the bottom of the hexagram) symbolize the inner
world and Lines 4, 5 and 6 symbolize the outer world. The 1st 2nd and
3rd lines are involved in their own process. This is essential for the
lower trigram to be strong and able to support the upper trigram. 
The 4th, 5th and 6th lines, however, are looking across the channel – looking towards the other. The lower trigram lines do not even know there is something on the other end of the channel (unless they bang into it). It is this awareness of the other side that makes the 4th, 5th and 6th lines transpersonal. They are aware of the other because they are looking. The have the foundation that the lower trigram has built and they are ready to use it as support to go outwards.
In looking at the two trigrams don't forget the harmony of the lines since you will see that they share common elements.
The Fourth Line - Externalization:
When you move from the 3rd line to the 4th line you move from the lower trigram to the upper trigram. Even though the 4th line is in the upper trigram it acts as a middle point between the two trigrams.
The 4th line is where the gene makes a half turn on the helix, giving it a view of the lower and the upper lines. It has a facility to pass information from the lower to the upper and vice versa. They do this by externalizing whatever is going on in their own lives – almost in a kind of ‘in your face’ way. They can’t wait to tell others all about everything, and they’re not all that concerned with whether or not the other is interested in what’s being externalized. Think of the missionary spreading the word of god as an example.
In Gate 62, the 4th line plays out this role in a fashion that, on the surface, doesn’t seem to embody this need to externalize. You see, the 62.4 KNOWS that it is getting an opinion from the 17. But it also knows that it takes time to get the details of the opinion right. Remember this is in the Logic circuit, so if you don’t get the details right you’re going to get a lot of complaints. So it acts as a mid-point between the need of the lower hexagram to get the right foundation and the upper trigram's need to get that foundation out there.
Here is an example of the harmony between the 1s and 4th lines. The 1st line is doing the research, the study, forming a meaningful opinion. The 4th line has to examine that opinion, and make sure all of the details are correct before it can externalize it. It’s a bit like study. If you ask the 17.4 for details before it’s ready it simply says “I know I have to get this out, but don’t bother me I’m still thinking”. Whereas the 17.1 would simply say, "Don't bother me, I'm thinking." - No mention of getting it out.
The 17.4 can’t successfully take advantage of any opportunity (a key word for 4th lines) until it has finished checking the details. Once it has the details in hand and an opportunity presents itself then it can externalize the complete, organized packaged. You can see in this that the thrust of the 4th line is putting things out, yet still colored by a respect of the 1st line theme.
Self Study: Look at your fourth lines and combine the keynote with the keynote of the gate. Share your thoughts in the Forum.