A conditional construction is made of two clauses, not merely two isolated verbs.
● The first clause is the condition (شرط).
● The second is the answer/consequence (جوابِ شرط یا جزاء).
The condition is a verbal clause. The answer can be a verbal clause or a nominal clause.
In لَوْ ذَهَبْتَ لَذَهَبْتُ, both parts are verbal.
In إِنْ تَجْتَهِدْ فَالنَّجَاحُ قَرِيبٌ, the condition is verbal, while النَّجَاحُ قَرِيبٌ is a nominal answer. The فَـ links that nominal answer to the condition.