Full happiness means full freedom. As long as we are not fully happy, we are chained, we are trapped and we are not free. Only in full happiness are we actually free. Therefore, only in Krsna consciousness we can be really free, because nowhere else are we able to be fully happy.
So this is nice to remember that devotional service is voluntarily performed. It is performed out of free choice and no one is forced in this way. Service can be our life, but this is our choice because Krsna does not force us! He gives us a choice; to simply serve or not, as we individually desire. But in devotional service, we are voluntarily taking responsibility. And that responsibility will bind us. But at the same time, we can give all of that up in any moment. This is because we are not signing any contract, we are not obligated. We can go away at any time we want. Who can stop us? But somehow or other we accept responsibility for Krsna because we desire it, because we wish to do so. Because we know that Krsna is worthy.