There were two major influences on Beecher's spiritual development. The first influence was that of a family gardener, a black serving man. As often happened in earlier eras during which keeping warm was a larger problem than it is now in the West, young Henry shared a bed chamber with this family servant. Each night this gardener would read his Bible in bed. He would comment and even laugh to himself about what he read. During this time, Henry heard Scripture read aloud, observed sincere piety, witnessed spiritual joy and gained a perspective that contrasted with his father's strict and unyielding Calvinist theology.
The second influence occurred while he was at Amherst College. Revivalist George Finney held meetings and, more importantly, befriended Henry's father, Lyman Beecher. The result of Finney's revivalist influence is that Henry Beecher suddenly felt his ungodly state yet had no understanding of how to remedy his condition. It is the resulting triumph over spiritual confusion that finalized Henry Beecher's religious/spiritual transformation quietly begun by a servant gardener in a shared bed chamber then carried on, less quietly, at revival meetings.
Although I am not sure exactly what it was, it seems that Beecher underwent a significant religious experience in the woods when he was in seminary school.
One May morning, alone in the Ohio woods, however, Beecher underwent a religious experience which shaped his ideas about God. (enotes)
This experience clearly shaped his own view of God, and led him in the direction of ensuring that he made religion palatable and understandable to all. Basically, Beecher did not feel comfortable with religion until he was able to find his own way to an understanding and appreciation.