"Messiah. They could tell what they knew; what they themselves had seen, and heard, and felt of the power of Christ. This is what everyone can do whose heart has been touched by the grace of God. John, the beloved disciple, wrote: “That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled, of the Word of life; ... that which we have seen and heard declare we unto you.” 1 John 1:1-3 . As witnesses for Christ, we are to tell what we know, what we ourselves have seen and heard and felt. If we have been following Jesus step by step, we shall have something right to the point to tell concerning the way in which He has led us. We can tell how we have tested His promise, and found the promise true. We can bear witness to what we have known of the grace of Christ. This is the witness for which our Lord calls, and for want of which the world is perishing. DA 340.1"
"That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled, of the Word of life; (For the life was manifested, and we have seen it, and bear witness, and shew unto you that eternal life, which was with the Father, and was manifested unto us;) That which we have seen and heard declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ."
Ellen White directly references 1 John 1:1-3 in this passage.
"Though the people of Gergesa had not received Jesus, He did not leave them to the darkness they had chosen. When they bade Him depart from them, they had not heard His words. They were ignorant of that which they were rejecting. Therefore He again sent the light to them, and by those to whom they would not refuse to listen. DA 340.2"
"That ye may be the children of your Father which is in heaven: for he maketh his sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust."
Both passages deal with God/Jesus extending grace even to those who reject Him. The EGW passage illustrates this principle with the Gergesenes, while the Matthew verse states the general principle of God's impartiality in blessing both good and evil.
"In causing the destruction of the swine, it was Satan's purpose to turn the people away from the Saviour, and prevent the preaching of the gospel in that region. But this very occurrence roused the whole country as nothing else could have done, and directed attention to Christ. Though the Saviour Himself departed, the men whom He had healed remained as witnesses to His power. Those who had been mediums of the prince of darkness became channels of light, messengers of the Son of God. Men marveled as they listened to the wondrous news. A door was opened to the gospel throughout that region. When Jesus returned to Decapolis, the people flocked about Him, and for three days, not merely the inhabitants of one town, but thousands from all the surrounding region, heard the message of salvation. Even the power of demons is under the control of our Saviour, and the working of evil is overruled for good. DA 340.3"
"Howbeit Jesus suffered him not, but saith unto him, Go home to thy friends, and tell them how great things the Lord hath done for thee, and hath had compassion on thee."
EGW's passage directly alludes to Mark 5:19, where Jesus instructs the healed man to go home and tell his friends what the Lord has done for him. EGW expands on this idea, explaining how the healed men became witnesses to Jesus' power and opened the door for the gospel in the region.
"And we know that all things work together for good to them that love God, to them who are the called according to his purpose."
The EGW passage illustrates the principle of Romans 8:28, that God can bring good out of evil. The destruction of the swine, intended by Satan for harm, ultimately led to the spread of the gospel. The connection is more than just thematic, it's an application of the principle.