“All things.” Although the text does not say so, we learn from the content of what Jesus is saying that he has stopped his prayer and has started speaking to his disciples.
“really knows...really know.” The Greek word is epiginōskō (#1921 ἐπιγινώσκω) an intensified form of ginōskō (#1097 γινώσκω). At that time in Jesus’ ministry, no one really understood the Son except the Father, and no one really knew and understood God but the Son and those people to whom the Son revealed Him, such as Jesus’ close disciples. All one has to do is look at the misguided doctrine and behavior of the Pharisees and Sadducees to know they did not “really know” God. They knew things about Him, but they did not “really” know Him. That is still true today. Many people know some things about God, but do not “really know” Him.
“anyone to whom the Son determines to reveal him.” This verse is not saying that Jesus picks and chooses who gets to know about God, including some and excluding others apart from that person’s desires. God wants everyone to know Him, and calls them fools if they do not (Jer. 4:22). Jesus Christ came to make known the Father (John 1:18), and expended himself trying to get people to understand both him and his Father. Jesus went so far as to say that people could see the Father by seeing him (John 14:9). God also makes it clear that He wants everyone to fully know the truth (1 Tim. 2:4). Nevertheless, many people do not know God. They do not know Him because they do not want to know Him, something they express by both their words and actions. John 3:20 says that people who practice evil will not come to the light. Also, we must keep in mind that when someone does not love God or want God in his life, God honors that. Similarly, when someone loves God, that is honored also, and Jesus says he will show himself to that kind of person (John 14:21).
“determines.” The Greek is boulomai (#1014 βούλομαι), and it means, to deliberately desire, will, or purpose something. To plan. Although it can be used of desire or want, it is somewhat different than thelō, which more refers to “want” or “desire.” Thus, boulomai includes “the thought of ‘purpose, intention, not mere will, but will with premeditation’” (Moulton and Milligan, Vocabulary of Greek NT). This verse is very similar to Luke 10:22, but Luke uses ginōskō instead of epiginōskō for “know.” Jesus knew the people and he knew who was honestly seeking to know God and who did not but was hypocritical.