Pentecost made all the difference. The disciples carefully examined their own hearts during the 10 days in the Upper Room. They understood their weakness and pleaded for His (JESUS) strength.

“As the disciples waited for the fulfillment of the promise, they humbled their hearts in true repentance and confessed their unbelief. As they called to remembrance the words that Christ had spoken to them before His death they understood more fully their meaning. Truths which had passed from their memory were again brought to their minds, and these they repeated to one another. They reproached themselves for their misapprehension of the Saviour. Like a procession, scene after scene of His wonderful life passed before them. As they meditated upon His pure, holy life they felt that no toil would be too hard, no sacrifice too great, if only they could bear witness in their lives to the loveliness of Christ’s character. Oh, if they could but have the past three years to live over, they thought, how differently they would act!” ( The Acts of the Apostles, p.36).
As the disciples prayed together, with humbled hearts before God, the Holy Spirit brought to their minds the lesson of humility, trust,submission and service that Christ longed for them to understand. The Holy Spirit not only convicts us of sin, He  heals our broken hearts. He brings us hope. He assures us that God has a better plan for our lives, and inspires us with promises of a better future. “All of you be submissive to one another, and be clothed with humility, for“God resists the proud, But gives grace to the humble.” Therefore humble yourselves under the mighty hand of God, that He may exalt you in due time”  (1 Peter 5:5-6)

Excerpt from 10 Days in the Upper Room by Mark A. Finley, p.63

The Acts of the Apostles, p.36 by Ellen G. White