What is meant by the following passage:

Cut is the branch that might have grown full straight,
And burned is Apollo's laurel-bough,
That sometime grew within this learned man.
Faustus is gone: regard his hellish fall,
Whose friendful fortune may exhort the wise,
Only to wonder at unlawful things,
Whose deepness doth entice such forward wits
To practise more than heavenly power permits.