1. Growth in spiritual knowledge. Often times I have learned something new about God or His Word from sitting under sound preaching in a church. Pastor's do a wonderful job of expounding on the passages and illuminating on the meaning and application of the verses preached on. Some will try and say that they "get fed" watching preachers on a Christian television station. I can tell everyone from experience that sitting around listening to Joel Osteen or any other televangelist wolf in sheep's clothing will NOT result in spiritual growth.
2. Accountability and Encouragement. We as Christians need other believers in our lives to hold us accountable and encourage us in our faith. Where is the best place to get that accountability? In a church setting. When we surround ourselves with believers instead of unbelievers, we will be encouraged to die to self and seek God's will in our lives. Not only do we need accountability and encouragement, but other Christians do as well and we can offer that same help to others. We can be an encouragment and challenge them to go further in their walk with Christ.
3. Corporate Prayer and Worship. There is something special about coming together with other believers to worship and pray. We are united in our praise to God, our crying out to God and it unifies us to the body. This, in my opinion, gives us a taste of heaven, coming together to praise and commune with the Creator of the universe.
4. Opportunities to serve others. Church attendance does not have to just benefit ourselves. We can benefit others. Getting connected to a church gives us opportunities for serving our brothers and sisters as well as our community. It gives us a chance to reach out to others and help them whether it is with a physical need or with prayer or the gospel. This allows us to act out our faith with others by being "doers of the Word" as opposed to just "hearers".
There are so many reasons getting connected to and attending a local church is important. It is not only important to a person's individual walk with the Lord, but with those around them as well. Whether you are attending Sunday mornings, evenings, Wednesday night, or some other day and time, it is vital to maintain a connection in a solid, bible-preaching church and be among like-minded believers.