يجب على المستأجر أن يجدد عقد الإيجار قبل أن ينتهي.

Because يجب is often used as an impersonal expression meaning it is necessary or it is obligatory.

So:

• يجب على المستأجر أن يجدد... = The tenant must renew...
• Literally: It is obligatory on the tenant to renew...

The preposition على is very common here to mark the person who has the obligation.

So يجب المستأجر would not be the normal way to say this.

أن introduces a following verb clause, similar to to in English in structures like must renew / to renew.

After أن, the present-tense verb goes into the subjunctive mood.

So:

• أن يجدد = to renew / that he renew

In fully vowelled Arabic, it would be:

• أَنْ يُجَدِّدَ

The final -a sound shows the subjunctive, but in normal unvowelled writing you usually do not see that ending.

يجدد comes from the verb جدد, which means to renew.

This is a Form II verb. A common feature of Form II is the doubled middle consonant, shown by the shadda:

• past: جدد
• present: يجدد

So the pattern itself often gives a more intensive or causative meaning compared with the basic root idea. Here the meaning is simply renew.

This is an iḍāfa construction, often called a genitive/possessive construction.

• عقد = contract
• الإيجار = the rent / leasing

Together:

• عقد الإيجار = the lease contract / the rental contract

In an iḍāfa:

1. the first noun usually does not take ال
2. the second noun can be definite
3. if the second noun is definite, the whole phrase becomes definite

So عقد الإيجار is correct.
العقد الإيجار is not the normal structure.

Here قبل أن means before ... happens or before ... ends.

So:

• قبل أن ينتهي = before it ends

This is a very common pattern in Arabic:

• قبل أن + present verb
• بعد أن + verb
• من دون أن + verb, etc.

Just like with أن يجدد, the verb after أن is in the subjunctive:

• يَنْتَهِيَ in full vocalization

The subject is understood to be عقد الإيجار.

So the meaning is:

• before the lease contract ends
• or more naturally in English, before the lease expires

Arabic often leaves out a repeated subject if it is already clear from context.

If you wanted to make it fully explicit, you could say:

• قبل أن ينتهي عقد الإيجار

But in the original sentence, the omitted subject is easy to understand.

Because the verb form already includes an implied subject.

• يجدد = he renews / he should renew

In this sentence, that implied he refers back to المستأجر.

So Arabic does not need to say the noun again unless there is a reason to emphasize or clarify it.

That is very normal in Arabic: once the person is clear, the verb can carry the subject information by itself.

It can mean either:

• the tenant in a specific context, or
• the tenant in a general legal/instructional sense

In formal Arabic, especially in contracts, laws, and official instructions, the definite article is often used for roles such as:

• المستأجر = the tenant
• المالك = the owner
• الموظف = the employee

So this sounds very natural in legal or formal language.

Yes, that is also grammatical and natural.

Compare:

• يجب على المستأجر أن يجدد عقد الإيجار...
• يجب أن يجدد المستأجر عقد الإيجار...

Both mean roughly the same thing.

The version with على المستأجر is especially common in formal or legal style because it clearly marks the obligation as falling on the tenant.

So the original sentence sounds a bit more official or contractual.

A fully vowelled version would be:

يَجِبُ عَلَى الْمُسْتَأْجِرِ أَنْ يُجَدِّدَ عَقْدَ الْإِيجَارِ قَبْلَ أَنْ يَنْتَهِيَ.

Some useful points:

• يَجِبُ: final -u nominative ending
• الْمُسْتَأْجِرِ: -i because it comes after the preposition على
• يُجَدِّدَ: subjunctive after أن
• عَقْدَ: accusative as the direct object of يجدد
• الْإِيجَارِ: genitive because it is the second noun in the iḍāfa
• قَبْلَ: accusative adverbial form
• يَنْتَهِيَ: subjunctive after أن

In normal everyday writing, these short vowels are usually omitted, but knowing them helps you understand the grammar.

Literally, ينتهي means ends or comes to an end.

But in the context of a contract, English often uses the more natural word:

• expire

So:

• قبل أن ينتهي = literally before it ends
• more natural legal English: before it expires

Both capture the idea, but expire is often the best English choice for contracts, permits, and agreements.