Does God desire not sacrifice?

Psalms 51:16 (KJV)

For thou desirest not sacrifice; else would I give it:
thou delightest not in burnt offering.

Ah yes, God only sees the heart. Our service to God doesn't matter. Attendence and participation don't matter. God only sees the heart.
Samuel even said, "Hath the Lord as great delight in burnt offerings and sacrifices, as in obeying the voice of the Lord? Behold, to obey is better than sacrifice, and to hearken than the fat of rams." 1Sam 15:22

Really?

In the first place, the whole point of this Psalm is a humbled and contrite David, fully realising his folly in the incident of Bathsheba, pouring out his heart to God. It simply highlights the fact that, repentance has to come out of godly sorrow (c.f. 2Co 7:10).
Secondly, if we just read all the way to the end, we find in the concluding verse 19
"Then shalt thou be pleased with the sacrifices of righteousness, with burnt offering and whole burnt offering:
then shall they offer bullocks upon thine altar."

As in the case of Samuel rebuking Saul, the problem is not with the sacrifice but with the motivation behind it. The issue is not that sacrifice is not important but that they must come out of a pure heart and in obedience to God's Word.

Yes, God sees the heart and it is precisely so that we need to render our perfect obedience AND offer our sacrifice and service that it may be acceptable to Him. And yes, far be it for us to put the cart before the horse by thinking we can make oursleves right by working on our own terms.