The fear of the Lord is the beginning of wisdom, Psalm 111:10

This means that without fear of the Lord, a person cannot even begin to be a little wise. 

It also means that a person without fear of God will not make a great discussion partner on the topic of God's merciful rescue through Christ Jesus. If you are preaching the Gospel to people who don't fear God, it would make sense to help them first of all with learning to fear God. 

Why can't a person become even a little wise if they do not fear God? A good explanation is provided in the New Testament, in the Letter to the Romans. Paul describes that God deprives wisdom from those who do not properly honor God. The foolishness and unintelligence of the ungodly is one of 20+ proofs of God's wrath "over all ungodliness and unrighteousness of people, who suppress the truth in unrighteousness", listed in Romans 1:18-31. 

Christians must still honor all people, and all earthly authorities, whether they are godly or ungodly. There is no license to point out any manifestation of unwisdom in for example a government authority, for whom instead Christians are to give thanks, prayers, petitions and intercessions before God (1 Timothy 2:1). 

How can people come to fear God? Recognizing the evidence of God's wrath is a good start. A person lacking fear of God will manifest in their own lives one or all of the types of wrath listed in Romans 1:18-31. 

God's wrath shown on earth ought to act as a forewarning of God's eternal wrath, which is promised at the time of God's eternal judgement for all who have not believed in Jesus.