lead on to, therefore, then
爰 centers on a logical or sequential connection: leading from one thing to another, expressing consequence (therefore), or indicating a next step (then).
The historical origin of 爰 is uncertain. It may have originally depicted a hand pulling or leading something, but the modern form is highly stylized and the component relationships are not clearly established.
The top 爫 looks like a hand reaching down, the middle 一 is a line or connection, and the bottom 友 suggests a friend or companion. Imagine a hand leading a friend along a path, showing the way forward: therefore, then.
For エン, picture the hand leading to an end: end -> エン, and the path leads on to the conclusion.