There are rewards in heaven.
Should they be a motivation to obey God?

If they were the lone
motivation, the obedience might not be real. And of course that would be known
by God.

If these rewards are
connected with our love for God and love for others, they are  a
promise given by God and should be rejoiced in. Here are a few of the promised
rewards:

“He who receives you receives
me, and he who receives me receives the one who sent me. Anyone who receives a
prophet because he is a prophet will receive a prophet’s reward, and anyone who
receives a righteous man because he is a righteous man will receive a righteous
man’s reward. And if anyone gives even a cup of cold water to one of these
little ones because he is my disciple, I tell you the truth, he will certainly
not lose his reward” (Matthew 10:40-42).

“Those who are wise will
shine like the brightness of the heavens, and those who lead many to
righteousness, like the stars for ever and ever” (Daniel 12:3).