Verse 18 is a perfect Trinitarian verse: all members of the Godhead are here. ‘Through him,’ that is through Christ who has been the subject of the passage up till now.
We have intimate access to the Father. As we pray, we are assured that God hears us on high, and the more we pray from sincere hearts, the more we sense it. We call him Father. We never fail to name the name of Christ who secured this access for us. We come with great reverence. He is our Father – Abba Father, our familiar Father – but there is always reverence and great earnestness. We sometimes have emergency prayers, but we never take prayer lightly. The greatest treasure in our lives is to be able to call upon God.
Is there a difference between Jews and Gentiles in the kingdom of heaven? No, both Jew and Gentile have equal access. It is sad, but there are Christian people (and good Christian people and many good expositors too), who never fully grasp this. Their idea is that the Jew is the first-class citizen in the church of Christ, and the Gentile is the second-class citizen. They think there is still something very special about the Jew, even though the apostle says it over and over again through his epistles that there is no difference, indeed, the whole Bible does.