When they saw the boldness of Peter and John, and perceived that they were unlearned and ignorant men, they marvelled; and they took knowledge of them, that they had been with Jesus. Acts 4:13. RC 42.1
Ever since the fall of Adam, Christ had been committing to chosen servants the seed of His Word, to be sown in human hearts. During His life on earth He had sown the seed of truth, and had watered it with His blood. The conversions that took place on the Day of Pentecost were the result of this sowing, the harvest of Christ's work, revealing the power of His teaching.... RC 42.2
Under the training of Christ the disciples had been led to feel their need of the Spirit. Under the Spirit's teaching, they received the final qualification, and went forth to their lifework. No longer were they ignorant and uncultured. No longer were they a collection of independent units or discordant, conflicting elements. No longer were their hopes set on worldly greatness. They were of “one accord,” “of one heart and of one soul” (Acts 2:46; 4:32). Christ filled their thoughts; the advancement of His kingdom was their aim. In mind and character they had become like their Master, and men “took knowledge of them, that they had been with Jesus.” RC 42.3
Pentecost brought them the heavenly illumination. The truths they could not understand while Christ was with them were now unfolded. With a faith and assurance that they had never before known, they accepted the teachings of the Sacred Word. No longer was it a matter of faith with them that Christ was the Son of God. They knew that although clothed with humanity, He was indeed the Messiah, and they told their experience to the world with a confidence which carried with it the conviction that God was with them. RC 42.4
They could speak the name of Jesus with assurance; for was He not their Friend and Elder Brother? Brought into close communion with Christ, they sat with Him in heavenly places. With what burning language they clothed their ideas as they bore witness for Him! Their hearts were surcharged with a benevolence so full, so deep, so far-reaching, that it impelled them to go to the ends of the earth, testifying to the power of Christ. They were filled with an intense longing to carry forward the work He had begun. They realized the greatness of their debt to heaven, and the responsibility of their work. Strengthened by the endowment of the Holy Spirit, they went forth filled with zeal to extend the triumphs of the cross. The Spirit animated them and spoke through them. The peace of Christ shone from their faces. They had consecrated their lives to Him for service, and their very features bore evidence to the surrender they had made.—The Acts of the Apostles, 45, 46. RC 42.5