But David doesn't do this but instead is sincerely sad that Saul was dead because he has a bigger picture of his life than just immediate gratification. The king of God's people had been slain by their enemies and God's reputation was in question while his people appear in disarray. He grieves for the Lord's work and for himself and so we learn that there are times to grieve as well as times to rejoice. We aren't to dance through life as if nothing matters other than having a good time but we aren't to spend all our time being sad just because this life is full of sadness.
I was raised with Charley Brown and perhaps that is why I use the expression "good grief" some times. But what we find in this account is that a Christian is called on to grieve well. I think David does this. He is deeply saddened at these deaths but his grief does not stop him from taking care of business. That evening he executes the Amalekite for supposedly killing Saul. His grief might last all his life but his desire to serve the Lord over rules his grief from paralyzing him. So Paul says that we should not grieve as the world grieves.
But there is another part of his grieving process that I believe we should be careful to incorporate into our own experiences. In vs. 17 & 18 we read, "And David lamented with this lamentation over Saul and Jonathan his son", " and he said it should be taught to the people of Judah; behold, it is written in the Book of Jashar." 17 and 18 tell us a couple of things. First of all this is an official lament; it is written down and so expected that others should read it and thus it would be beneficial for them to think about it. A lament is a formal expression of grief and sorrow as opposed to spontaneous outpouring of emotions, 11-12. There is nothing wrong with spontaneity in such things of course, but David sees this as an opportunity to instruct God's people about the Lord.
The point to be made here is that it would be profitable, and perhaps we are being instructed here that it is the duty of all saints, to get to a point where they can use such things as a way to help others and glorify the Lord. Why not write down a lament and offer it up to God and if so led offer it up to others as well? We know that difficult times aren’t miraculously healed by God after a short time. It takes time to reflect on truth. A lament assumes that grief is ongoing and invites us to enter into the process.
And I don't think this applies only to the times we experience the death of a loved one. Many of the trials of life cause us to go through traumatic times in which God has much to teach us about himself. These also can be times in which we openly express what we have learned from the Lord so we can encourage others. As John Piper's popular book title suggests, "Don't Waste Your Life". Can we not apply this to seizing the opportunity to glorify the name of the Lord by the experiences he brings us through? To grieve as the world grieves is to waste your grief.