O Prophet (Muhammad), be on your guard lest you omit to recite some things which are being revealed to you feeling distressed in your heart that they might say: “Why has no treasure been sent down to him, or why has no angel come with him?” You should know that you are nothing but a Warner! It is Allah Who is the Custodian of everything.
Meaning:-
Omit: fail to mention, miss, pass over.
Distressed: sorrow, or pain.