What does the Bible say about sinning against the Lord?

The Bible clearly teaches that all sin is ultimately against God, not just against other people. As stated in 1 Samuel 2:25, when a man sins against the Lord, who will entreat for him? This signifies that sinning against God is a grave matter because it violates His divine justice and holiness. Even David, in Psalm 51:4, acknowledges, 'Against thee, thee only have I sinned.' Every wrongdoing towards others is also an offense to God, revealing our need for a mediator to stand in the gap for us.