There have been documented cases of people actually sweating drops of blood under extreme emotional pressure. This might explain why Luke is the only writer to mention the angel strengthening Him, He needed supernatural strength to endure His sufferings.
The use of the words "as it were" might also mean that the sweat of Jesus was only comparable to blood in consistency or size, but it tells of the effect Jesus' agony had on His physical body.
Jesus' sufferings for us were more than just physical. In the garden, before He suffered physically, He suffered emotionally, almost to the point of death. Luke records, an angel had to come and give Him strength or the emotional struggle alone would have killed Him.
All that Jesus did was motivated by love. It was for the joy that was set before Him that He endured going to the cross. He didn't do what He did to save us out of pity or a sense of obligation as our Creator. He did it because He loves us.
