Why Jesus resurrected by God after his death?

Because he was sinless, he did not earn death — “the wages of sin”, as the Bible calls it. So God raised him from the dead.

By raising the Lord Jesus from the dead, God showed all how He will reward all those who truly follow Jesus. If we put our faith in Christ and if we try very hard to obey and follow him, we, too, shall be raised from the dead at the last day (see topic ‘Ressurection’ for more).