The church exists for three purposes: The Glorification of God; The Edification of the Saints; And the Evangelization of the World. In other words, "Upward, Inward, and Outward."
The first purpose of the church is to exalt God (upward). God put us on this earth to know Him and to glorify Him. According to Ephesians 1:12, we are here to praise our glorious God! This is why we worship the Lord in song. Worship is an important part of service. A worship leader/team is not there to perform for you. They "perform" for an audience of One: God! And they are not a warm-up act either. They are here to lead us in worship. They are leading us in prayer set to song. That is why we should never be late to church. When we are late, we miss out on glorifying God together. He inhabits the praises of His people (see Psalm 22:3).
One of the most powerful things I had ever seen when I first came to church was worship. Back in those days, the choruses and chords were very simple, but the worship was positively supernatural. Did you know that your worship is a witness? Acts 2:47 says that the early church was "praising God and having favor with all the people. And the Lord added to the church daily those who were being saved" (NKJV). There was a direct connection between worship and witness. We are being watched, both inside and outside the walls of our church. The outside world marvels when a child of God can rejoice in hardship.
Sitting next to you on any given Sunday may be a visitor or a nonbeliever. They are essentially sizing everything up by what they see. Not just what happens on the platform, but the people around them. During times of worship, do you sing out to the Lord? Or did you sit in silence? Worse yet, do you talk with the person next to you or spend the time texting? What message are you sending to those visitors? Can you not tune those things out and just glorify God?
When we glorify God in church with other believers, it gives us perspective. When we come to God in prayer and in worship, we see things correctly. This is why Jesus taught us to pray "Our Father in heaven" (see Mathew 6:9 NKJV). It causes me to remember, whatever I am facing, that the all-powerful, all-knowing God of the Universe who loves me is listening to me right now. But when I isolate myself from other believers, I lose perspective. I can become fearful, confused, angry, and even bitter.
You recall when Jesus was crucified, the disciples initially scattered. But they quickly gathered together again to encourage one another. Thomas was not there and missed out on an appearance of Jesus. When told of it, he essentially said, "Unless I touch the wounds in His hands, I will not believe." But the next time they were meeting, Thomas was there and his perspective was quickly corrected.
Asaph was grappling with the age-old question, "Why do the wicked prosper?" And then it dawned on him. "When I tried to understand all this, it was oppressive to me till I entered the sanctuary of God; then I understood their final destiny. Surely you place them on slippery ground; you cast them down to ruin" (Psalm 73:16 NIV). Asaph is essentially saying, "I didn't understand why things are the way that they are until I came into God's presence to study His Word with His people. Then my questions came into a proper perspective."
Why should believers go to church? To exalt God-to reach upward.