Three cards: where it came from, where it stands, where it tends.
The three-card line is the workhorse of tarot: quick to lay, easy to read, and flexible. Read here as past, present and future, it gives a situation a direction of travel.
What lies behind the matter — the cause, the habit, or the event whose influence is still felt.
The situation as it is today: the centre of the line and the subject of the reading.
Where the present road leads. A direction of travel, not a fixed destination.
Read the line as a sentence. The middle card is the subject; the left is what brought it about; the right is where it tends if nothing changes. Look for a suit or number repeated across the three — that is the thread.