In our opening verse, Apostle Paul wasn't talking to people who didn't know about the Holy Spirit when he said, "...be filled with the Spirit." So, why then did he admonish them to be filled with the Spirit, even though they had already received the Holy Spirit? It's because receiving the Spirit and being filled with Him always are two different things.
Receiving the Holy Spirit is a one-off experience, but you're to get filled with the Spirit always! The same verse in the Amplified version says, "...ever be filled and stimulated with the Spirit"; that means be filled all the time.
The prophets of old didn't have this experience. They had the Holy Spirit come upon them occasionally. Today, the Holy Spirit doesn't just come on us, He lives in us; our spirits are immersed in Him, and we can be ever filled with the Spirit.
What a blessing this is! There're things you do that get you filled with the Spirit; for example, "Speaking to yourselves (not others this time) in psalms and hymns and spiritual songs, singing and making melody in your heart to the Lord" (Ephesians 5:19).
Never leave home or embark on any endeavour without being filled with the Spirit. A good way to always get yourself in the flow of the Spirit is speaking in other tongues. You can't be filled with the Spirit and be defeated in life; no! Your spirit will continually be energized for victory and success every day.
Make up your mind to be filled with the Spirit continually. It's not something you need only when you're faced with a problem or when you want to prepare for a special event; no. When the Bible tells us about being filled with the Spirit, it puts it in the continuous language. You ought to be perpetually high on the Holy Ghost, and walk in the Spirit, not sometimes, but ALWAYS!