Is it enough for me to watch a sermon online every Sunday? I have some Christian friends that I spend time with and we pray together sometimes. I study the Bible on my own and listen to my favorite preacher online every week. What need would I have to get up and go to a brick and mortar church every Sunday?
This depends on what your church services provide for you and your own life situation.
As a Catholic, I can't really do that because I cannot receive Eucharist at home, unless a priest comes over, in which case I could. But this doesn't lend itself well to internet services.
Another common reason people go to a service is because of fellowship and community worship. You may fellowship via the internet with others but you don't get the day-to-day interaction online that you may in person. The dynamic is different. Also, it is a different experience worshiping in a group vs. alone. It is very important for a Christian to build relationships with other Christians because it provides some support and an avenue for growth in your faith. Church services are a major way to fill that need.
I would say that if you don't have any better options, or you physically are unable to make it to your service on Sunday, having an online service may fill that void. Many elderly even watch church services on TV if they are homebound.
I personally do them in addition to going to a physical church. They can be worth it. But I would only replace a physical service with an online one out of necessity, myself.
Searching what the Bible has to say about this, I came upon Hebrews 10 : 25
5 Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching.
It depends on , does being on the internet qualify as "assembling"? Looking up the meaning of "assembling", we get:
bring together or gather into one place, company, body, or whole. (Emphasis my own)
It's pretty clear therefore, that going to a place where there are other believers is necessary. That doesn't necessarily mean a church, it could be a house, or a field, but as long as there are other believers gathered together at that location worshipping the Lord, that's fine.
I looked this up on its Greek origin, that is, the Greek word behind "assembling", and I found it came from:
ἐπισυναγωγή gathering together , assembling together
Thus, the dictionary reference above would be quite dependable.