It already has.
The grace of God has already been given to us, just as every spiritual gift in the heavens (Ephesians 1) has. Titus 2:11 says that the grace of God has already appeared.
Why do we need to wait sometimes for grace to seemingly ‘kick in’?
Why? Because grace has already kicked in.
When something needs to change in your life, your desires change. You decide, sooner or later, to pray about it and ask God to make it happen.
Because of the grace of God that has already given you, when something needs to change, it will change, naturally. It starts with a realization: This needs to change. Then, sooner or later, a prayer: Lord, please make this change. Then, at some point, the change.
You might need to do something. Ask the Holy Spirit about that, and don’t be confused or in torment about it. God hasn’t given you a spirit of fear, so don’t be afraid.
Perhaps you need to go to a certain meeting or talk to a certain person and get them to pray for you. There’s no shame in that–the Bible tells us to respect body ministry and let the elders of the church pray for you (James 5:14).
Perhaps you need to change a certain habit, such as when one needs to lose weight. (author silently raises his hand). Maybe your eating habits need to change, and you need grace for that.
Perhaps you need to do nothing at all, except continue to pray and wait. While you’re waiting, you might meditate on Bible verses about grace (I mentioned a couple above, but there are plenty more). Pray in tongues if you know how, because that strengthens your spirit (1 Corinthians 14:4).
Above all, know that grace is already at work within you. Trust that God’s grace is enough for you (2 Corinthians 12:9) and that you will get through.