"In the time of John the Baptist, Christ was about to appear as the revealer of the character of God. His very presence would make manifest to men their sin. Only as they were willing to be purged from sin could they enter into fellowship with Him. Only the pure in heart could abide in His presence. DA 108.1"
"Blessed are the pure in heart: for they shall see God."
The EGW passage echoes the sentiment of Matthew 5:8, focusing on the necessity of purity for fellowship with God. It's not a direct quote, but the theme is clearly present.
"Then said I, Woe is me! for I am undone; because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips: for mine eyes have seen the King, the Lord of hosts."
Both passages deal with the unworthiness felt when encountering the divine. Isaiah's reaction to seeing God is paralleled in the idea that Christ's presence reveals sin.
"Thus the Baptist declared God's message to Israel. Many gave heed to his instruction. Many sacrificed all in order to obey. Multitudes followed this new teacher from place to place, and not a few cherished the hope that he might be the Messiah. But as John saw the people turning to him, he sought every opportunity of directing their faith to Him who was to come. DA 108.2"
"Then went out to him Jerusalem, and all Judea, and all the region round about Jordan, And were baptized of him in Jordan, confessing their sins."
The EGW passage describes the large crowds following John the Baptist, which is directly supported by the description in Matthew 3:5-6.