Muhammad is the Messenger of God and those with him are stern to the disbelievers yet kind among themselves. You can see them bowing and prostrating before God, seeking His favors and pleasure. Their faces (foreheads) are marked due to the effect of their frequent prostrations. That is their description in the Torah and in the Gospel they are mentioned as the seed which shoots out its stalk then becomes stronger, harder and stands firm on its stumps, attracting the farmers. Thus, God has described the believers to enrage the disbelievers. God has promised forgiveness and a great reward to the righteously striving believers.