These are Jesus' words to Peter when Peter told Jesus he wouldn't let him die. Any of us can be a stumbling block.
it is inevitable that stumbling blocks come; but woe to that man through whom the stumbling block comes! Matthew 18:7
Set your mind on God and living for Him. He'll keep you from being a stumbling block to a fellow Believer.
If you do this rightly though, know that you will be a stumbling block to those who have rejected God. They will stumble over you. And this is okay. Actually, this is quite good because by stumbling over your light, maybe it will cause them to land flat on their backs and look up to God.