A single sentence may contain two different lams. Read the meaning of each clause before deciding.
● You should worship your Lord so that He may forgive your sins.
فَلْتَعْبُدُوا رَبَّكُمْ لِيَغْفِرَ لَكُمْ ذُنُوبَكُمْ
First lām: Lam al-Amr. Second lām: Lam Kay.
● They should help the Muslims.
لِيَنْصُرُوا الْمُسْلِمِينَ
Context supplies the “should” meaning.
● We should help Allah so that He may help us.
لِنَنْصُرِ اللَّهَ لِيَنْصُرَنَا
The first underlying jussive form ends in sukun; connected reading gives a temporary kasrah before اللَّهَ.