Verse 18 is the key to understanding the mystery behind this prophetic-psalm. Yes, this is a processional-psalm in the fact that David is writing of the Lord’s triumphant leading his people from Mount Sinai to Mount Zion, and from the tabernacle to the temple with “May God arise…extol him who rides on the clouds (meaning cloud of smoke during the day).” However, verse 18 in mystery says, “When you ascended on high, you took many captives; you received gifts from people, even from the rebellious – that you, LORD God, might dwell there.” For David and the generations till the Messiah’s arrived this would have been mysterious.
However, the Holy Spirit revealed to the first church, as recorded by Apostle Paul’s letter to the Ephesians, the revelation of this verse, and thus this psalm. “But to each one of us grace has been given as Christ apportioned it. This is why it says: “When he ascended on high, he led captives in his train and gave gifts to men.” (What does “he ascended” mean except that he also descended to the lower, earthly regions? He who descended is the very one who ascended higher than all the heavens, in order to fill the whole universe.) It was he who gave some to be apostles, some to be prophets, some to be evangelists, and some to be pastors and teachers, to prepare God’s people for works of service, so that the body of Christ may be built up until we all reach unity in the faith and in the knowledge of the Son of God and become mature, attaining to the whole measure of the fullness of Christ.” (Ephesians 4:7-13)
We have a magnificent reason to praise Jesus, the king who descended, being found in the form of a man, dying, rising to life, clothed in glory, and is seated at the right hand of God. He sent the Holy Spirit and appointed tasks to his people. These tasks are not for selfish gain. The tasks that the ascended Christ gives is for the benefit of his people, the church. Jesus dwells on in heaven and fills heaven and earth. Jesus does not want his people to be children forever. He wants us to be mature in all things. We are to build each other and self in love. (Ephesians 4:14-16)

