Reassurance first, and then the call back

Look at the structure, because it is unusual and it is deliberate.

The first verse is addressed to people who have already gone badly past the line. Not to people who are thinking about it. It tells them not to lose hope, and it does not attach a size limit to the sins it is talking about. Then, and only then, the next verse says to turn back.

So it is not a licence, which is what its critics worry about, and it is not a standalone comfort, which is what it usually gets used as. It is the door being held open first, so that walking back through it is possible at all.

The same claim is made elsewhere without the vocative and without the raised voice. Anyone who does evil or wrongs his own soul and then asks God for forgiveness will find Him most forgiving and merciful. The only condition in that sentence is the asking, and you have done that already, many times. Another opens with peace, and says that your Lord has taken it upon Himself to be merciful. Mercy there is written on His side of the ledger. It is not something you have to prove you deserve.

That structure, reassurance before demand, is the structure of this lesson, and we did not invent it.