Raised in a Calvinistic Methodist home, he was a devout child who attended church regularly and memorized scripture at night.
Roberts was known as a young man who spent many hours praying each week both personally and at group prayer meetings.
His involvement in the Welsh revival followed a period of religious awakening across the region, but most biographies assert that "its spark seemed to fly from Roberts.
"[citation needed] He reported having experienced visitations from the Holy Spirit depicting "all Wales being lifted up to Heaven," at one time asking his roommate (and later brother-in-law) if he believed that God could then "give us 100,000 souls.
Attendance at a service held by evangelist Seth Joshua in Blaenannerch, Cardiganshire led to an experience that formed Roberts' belief in the "Baptism of the Spirit".
In keeping with Roberts’ statements and beliefs, the most plausible theory for his isolation and seclusion may be that he grew concerned that his unsought celebrity status was attracting people to his meetings for the wrong reasons, and he desired that God, not himself, be glorified.
Morgan commented, "Since the [1905] revival, various Socialistic organizations have invaded the valleys and are gathering Welsh working men by the thousands to hear the 'socialistic gospel'.
There are accounts of how he continued the mission especially on his knees and with his publications (co-authored with Penn-Lewis) that encouraged the missionary growth of the 20th century.
Accusations of his having no theological or ministry training may have hindered his ability to stay on track amidst a clamour for his time.
Not only were people converted to a faith in Christ, but there were "signs" following his preaching, including healing the sick and casting out demons.
When he was asked to pray at his father's funeral in 1928, witnesses said his prayer was like an electric-like force, so great, in fact, that they thought revival would break out again.