If they never speak in tongues, then how can they build up their most holy faith?
Lots of ways. Study the Bible, pray, fellowship with like-minded believers, give, and more.
Please do not misunderstand me. I do believe in operating the manifestations, and I do believe that God would like all Christians to speak in tongues. But the fact is that most don't. I submit it's due to ignorance of what speaking in tongues is.
Also, do not be ignorant of the kingdom of darkness. Demons love to copy God. Think about it. They can do signs and wonders too (antichrist will do the same thing and they're not of God) . And, they can definitely speak in a counterfeit tongue.......google search it. If you're bold enough, watch a video of it on YouTube.
Christians speaking in tongues by the freedom of their will can't be counterfeited.