لِيَكْفُرُواْ بِمَا اتَيْنَاهُمْ
...
Then, when He has removed the harm from you, behold! some of you associate others in worship with their Lord (Allah). So they are ungrateful for that which We have given them!
It was said that the Lam here (translated as "So") is an indicator of sequence, or that it serves an explanatory function,
meaning, `We decreed that they would conceal the truth and deny the blessings that Allah has bestowed upon them. He is the One Who bestows blessings and the One Who removes distress.'
Then Allah threatens them, saying:
...
فَتَمَتَّعُواْ
...
Then enjoy yourselves,
meaning, do what you like and enjoy what you have for a little while.
...
فَسَوْفَ تَعْلَمُونَ
but you will soon come to know.
meaning the consequences of that.