Albert Barnes Commentary John 1:18

"No man hath seen God at any time; the only begotten Son, who is in the bosom of the Father, he hath declared [him]." — John 1:18 (ASV)

No man hath seen God at any time—this declaration is likely made to show the superiority of Jesus's revelation over that of any previous dispensation. Therefore, it is said that Jesus possessed an intimate knowledge of God, which neither Moses nor any of the ancient prophets had. God is invisible; no human eyes have seen Him. But Christ had a knowledge of God that, for our understanding, could be described as His having seen Him. He knew Him intimately and completely, and was therefore qualified to make a fuller manifestation of Him. See John 5:37; John 6:46; 1 John 4:12; Exodus 33:20; John 14:9.

This passage is not meant to deny that people had witnessed manifestations of God, as when He appeared to Moses and the prophets (Isaiah 6:1–13). Rather, it means that no one has seen the essence of God or has fully known God. The prophets delivered what they heard God speak; Jesus delivered what He knew of God as His equal, and as one who fully understood God's nature.

The only-begotten Son—see the notes at John 1:14. This verse shows John’s understanding of the meaning of that phrase, as denoting an intimate and full knowledge of God.

In the bosom of the Father—this expression is taken from the custom among Eastern peoples of reclining at their meals. See the notes at Matthew 23:6. It denotes intimacy, friendship, affection. Here it means that Jesus had a knowledge of God such as one friend has of another—knowledge of His character, designs, and nature that no other one possesses, and which therefore qualifies Him above all others to make God known.

Hath declared Him—this means He has fully revealed Him or made Him known. Compare Hebrews 1:1, Hebrews 1:4. This verse proves that Jesus had a knowledge of God superior to that of any of the ancient prophets, and that the fullest revelations of His character are to be expected in the gospel. By His Word and Spirit, He can enlighten and guide us, and lead us to the true knowledge of God. There is no true and full knowledge of God that is not obtained through His Son. Compare John 14:6; 1 John 2:22–23.