There are many reasons God has called His people to give to a local church. Here are a few:
God has called His people to honor Him for all He has given us by giving back our "first fruits". (1 Corinthians 16:1-2, Proverbs 3:9)
Giving to a church allows you to be a part of the vehicle that God has called to take His Gospel to His people. (1 Timothy 3:15)
Giving consistently helps us keep our minds on eternal things and helps keep idols out of our hearts. (Matthew 6:24)
*Giving online allows you to be consistent with your giving while enabling you to have security and transparency when you do give.