I think taking a day of rest each week is important, not only for our spiritual growth, but also because it holds an important spiritual parallel. On such a day we regularly set aside our own work and rest from it. In the same way, we are called to lay aside our own "works of righteousness" and rest in the grace of God. When we rest in His grace it's not like we're kicking back our heels and saying, "Okay, God, do Your work!" Instead we are seeking Him, growing closer to Him, enjoying Him, serving Him, and striving to glorify Him while resting in His grace, trusting Him to accomplish His work in and through us
. Similarly, when we take a day of rest we aren't literally sleeping all day but we go to church to seek Him, grow closer to Him, enjoy Him, serve Him by serving our fellow believers, and glorify Him
Again, I think it's important to take a day of rest but I think the subject should be far from debatable, as Paul said in Romans 14:5, "One person esteems one day as better than another, while another esteems all days alike. Each one should be fully convinced in his own mind." I thinking Paul was addressing that because it's so easy to simply go through the motions each week "because the Bible says . . .!" instead of making it a matter of the heart. When it becomes a debated subject it becomes a matter of what's right and wrong, making us focus on our "works of righteousness" instead of the true purpose. Personally, I don't think it matters between Saturday or Sunday, but if you feel strongly about a certain day then I respect you for acting upon your beliefs.