What was the extent of the Jewish believers' faith before Pentecost?
Before Pentecost, the Jewish believers' faith extended only to believing that Jesus was the Christ. That was all they were to believe: that He was who He said He was, as shown through His three years of signs, wonders, and miracles.
Les explains that these Jewish believers—the 120 plus however many others—had been able to believe only that Jesus was the Christ. That was the extent of their faith: He was who He said He was, as He demonstrated through His three years of signs, wonders, and miracles. At Pentecost, after this limited faith, they were all filled with the Holy Ghost and the Holy Spirit, and began to speak with other languages.
And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.